1472 lines
78 KiB
Plaintext
1472 lines
78 KiB
Plaintext
Newsgroups: rec.backcountry
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From: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
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Subject: [l/m 9/25/92] Water filters & Giardia Distilled Wisdom (9/28) XYZ
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Organization: NAS Program, NASA Ames Research Center, Moffett Field, CA
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Date: Sat, 9 Jan 93 12:20:20 GMT
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Message-ID: <1993Jan9.122020.2951@nas.nasa.gov>
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Reply-To: tut@sun.com (Bill Tuthill)
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Lines: 1461
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Panel 9
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Index:
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a. (Title?)
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[Comparison of filters, boiling and iodine]
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Filters: First Need, Katadyn,
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Boiling,
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Iodine: PolarPure, Potable-Aqua
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Bill Tuthill
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1991 - 1992
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Based on "Medicine for Mountaineering", owner's manuals and
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personal experience of author
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b. GIARDIASIS
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Memo from Center from Disease Control
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Dennis D. Juranek
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Chief, Epidemiology Activity
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Parasitic Diseases Branch
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Division of Parasitic Diseases
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Centers for Disease Control
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1990
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c. Back-country water treatment to prevent giardiasis.
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American Journal of Public Health
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December 1989, Vol 79, No 12, pp 1633-1637.
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Copyright 1989 AJPH 0090-0036/89$1.50 [used without permission]
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Filters: First Need, H2OK, Katadyn, Pocket Purifier, Water Purifier
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Chemicals: Polar Pure, Coghlan's Emergency Germicidal Drinking
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Water Tablets, Potable Aqua, 2% iodine,
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Sierra Water Purifier, Halazone, commercial liquid bleach
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Jerry E. Ongerth, PhD, PE,
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Ron L. Johnson,
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Steven C Macdonald, MPH,
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Floyd Frost, PhD,
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Henry H. Stibbs, PhD
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d. REI Water Filter Chart (2 similar articles)
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Comparison of specs: pore size, weight, capacity, filter life,
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cost/gallon, price, replacement cost,
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elements
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Filters: Katadyn, MSR, PUR, First Need, Basic Designs, Timber Line
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199x?
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Copyright (c) 1991 by Bill Tuthill
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Unpurified drinking water may contain four things that pose health risks:
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protozoan parasites (e.g. giardia), toxic bacteria, harmful viruses, and
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poisonous chemicals. Of the methods available in the field, only boiling
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and iodine are entirely effective against the first three, and only charcoal
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filtration is effective against the fourth.
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The First Need(R) water filter is cheap (less than $40), but is effective
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merely against protozoan parasites. Its .4 micron filter pores are smaller
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than giardia cysts at 3.5 microns, but larger than some bacteria, such as
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E. coli at .3 to .9 microns. The First Need's charcoal canister is not big
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enough to be effective against poisonous chemicals -- you need a pound of
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charcoal for this -- so it just adds unnecessary weight, and provides a
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potential haven for the growth of harmful bacteria. If you own a First Need
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filter, flush it with iodine after each trip.
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The Katadyn(R) water filter is expensive (over $200), but is completely
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effective against bacteria as well as giardia. Moreover, it can be cleaned
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after it clogs up. The Katadyn is effective at removing smaller bacteria
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such as E. coli. However, its .2 micron filter is not effective against
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any virus. If you travel abroad (to Nepal for example), you risk viral
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infections such as Hepatitis A and Hepatitis non-A non-B, among others.
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MSR has a new water filter, which may be superior to the Katadyn. Results
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from the field aren't in yet.
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To be entirely safe, water should be boiled for at least five minutes.
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Giardia is killed in less than a minute at 176 degrees, well under the
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boiling point. Bacteria and viruses last somewhat longer, but are probably
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killed in less than five minutes at 190 degrees. Some viruses may last
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longer; nobody knows. At 10,000 feet water boils at 194 degrees; above
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this altitude boil water about an extra minute for each 1000 feet.
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If you have neither the time nor the inclination to boil water, iodine
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is equally effective. After 15 minutes (30 minutes for very cold water),
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a sufficient dose of iodine kills all protozoa, bacteria, and viruses.
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One readily-available choice is Potable-Aqua(R) tablets. Dissolve one
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tablet per liter of water (two tablets if cloudy) and wait. The problem
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with iodine tablets is that they degrade upon contact with moisture, so
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keep that bottle dry, and discard it upon returning home.
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Avoid halazone and Clorox, because chlorine is volatile, slow to disinfect,
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and works differently against protozoa and viruses at various pH levels.
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It also reacts with organic compounds to form carcinogenic chloramines.
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Iodine is not highly toxic, and in fact is an essential ingredient of
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human nutrition. However, continuous ingestion of large doses may cause
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health problems, so don't iodinate all your water for more than a few
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months at a time.
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The accepted concentration for iodine disinfection is 8 milligrams per
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liter, but this is mostly to get rid of protozoan parasites. A good way
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to reduce overall iodine consumption and minimize that iodine flavor is
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to filter first, then use a low concentration of iodine to get rid of
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bacteria and viruses. For this, a concentration of .5 mg/L is deemed
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adequate, so one capful of PolarPure or one Potable-Aqua tablet should
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disinfect around 16 liters of lightly filtered water. The Timberline(R)
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filter, with its 2 micron pores, is fine for removing protozoa.
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Giardia has become a well-known, almost fashionable, outdoor hazard.
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Many people who experience gastro-intestinal problems after drinking
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bad water think they have contracted giardia. In many cases they have
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contracted something else. Since the only FDA-approved treatment for
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giardia (Flagyl) is very nasty, it's wise to make sure you really have
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giardia before taking Flagyl. Most low-grade bacterial infections go away
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on their own, and Flagyl is ineffective against viral infections. One
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alternative to Flagyl is quinacrine. In many parts of the world (Asia
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for example) Tinidazole is available, and is preferable to Flagyl because
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it is less toxic and quicker acting.
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[This information based on "Medicine for Mountaineering", various owner's
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pamphlets, and personal experience.]
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Addedum 1992
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A packet of information arrived recently from Recovery Engineering
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in Minneapolis, which I'll summarize as promised.
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They have a new product, the Pur Scout, which I believe is destined
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to replace the First Need as the most popular low-cost filter. It
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has the same 1 micron filter plus iodine matrix as the Pur Explorer,
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pumps a quart in 120 seconds, but weighs only 12 oz! Capacity is
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200 gallons, twice the First Need, but its $60 cost is less than
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twice as much. The Scout is not self-cleaning like the Explorer,
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and is only half the speed, with 2/5 the filter life.
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Unlike other water filters, all Pur products meet EPA's purification
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guidelines. No other filter does this, because no other filter can
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remove viruses. Here is the abstract from a study done at U Arizona
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on the Pur Tritek(tm) system:
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"Three identical [Pur Traveller water filters] were evaluated
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for their ability to inactivate/remove Klebsiella terrigena,
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poliovirus type1, rotavirus SA-11, and Giardia lamblia cysts.
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The units were operated according to the manufacturer's
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instructions until the designed lifetime of 100 gallons (378
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liters) passed through. The units were challenged with [the
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micro-organisms mentioned above] after a passage of 0, 50, 75
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and 100 gallons. At the 75% lifetime challenge, 'worst case'
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water quality of 1500 mg/l dissolved solids, 10 mg/l organic
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matter, 4 degrees C, with a turbidity of 30 NTU and a pH of 9
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was used. For the 100% lifetime test the worst case water
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quality at pH 5 was used. The units were also tested after
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stagnation for 48 hours at the 50%, 75%, and 100% [stages].
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"At 0 and 50% lifetime test points, > 99.9999% of the bacteria,
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> 99.9% of the Giardia cysts, and > 99.99% of the test viruses
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were removed. With worst case water two passages of the test
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water through the units was required to achieve these same
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removals. These units would comply with criteria guidelines
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suggested by the US EPA...
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"One passage of the pH 9 worst case water was not sufficient
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to remove the Klebsiella terrigena and poliovirus type1 to
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the required reduction. However, the required reduction [was]
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achieved by passage of the test water through the units a
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second time... Holding the water for 5 to 10 minutes after
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it had passed through the units also resulted in a further
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reduction of test bacteria and viruses."
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What is Klebsiella terrigena anyway? I assume it's a bacteria, but
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what disease does it cause? And what does NTU stand for? Also, is
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parts per million (ppm) the same as milligrams per liter (mg/l)?
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Here is the residual iodine in ppm after treatment:
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cup1 cup2 cup3
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0% .7 .7 .7
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50% .6 .5 .6
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75% .6 .6 .7
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100% .7 .6 .8
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This indicates that the filter still had plenty of life at 100 gallons.
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It also indicates that there is enough residual iodine to kill off all
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viruses and bacteria overnight (assuming ppm = mg/l). At these levels
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some iodine taste may be present, which can be removed with the optional
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charcoal filter. Since the charcoal filter also removes iodine, it
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would be prudent to use it only when filtering good quality water above
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5 degrees C. It's a tradeoff, though: when travelling thru agricultural
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areas, charcoal filtration helps remove pesticides and herbicides.
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All in all, I've decided to trade in my Katadyn for a Pur Explorer. I
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used an MSR last week on the Rogue, and liked its pump action and bottle
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attachment, but it *did* start to clog. Anybody want to buy my Katadyn
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(in excellent condition) for a mere $185? F*ck the Swiss.
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=====
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OCR'ed memo from the Center from Disease Control:
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GIARDIASIS
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GIARDIASIS: By Dennis D. Juranek, Chief, Epidemiology Activity
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Parasitic Diseases Branch
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Division of Parasitic Diseases
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Centers for Disease Control
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Transmission and Control
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Introduction
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During the past fifteen years giardiasis has been recognized as one of the
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most frequently occurring waterborne diseases in the United States (1).
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Giardia lamblia have been discovered in the United States in places as far
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apart as Estes Park, Colorado (near the Continental Divide); Missoula,
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Montana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; and Pittsfield
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and Lawrence, Massachusetts just to name a few. In light of recent large
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outbreaks of waterborne giardiasis, it seem timely to present reliable
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information on the way in which giardiasis is acquired, treated, and
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prevented.
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Giardiasis: Prevalence and Symptoms
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Giardiasis is a disease caused by a one-celled parasite with the scientific
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name Giardia lamblia. The disease is characterized by intestinal symptoms
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that usually last one week or more and may be accompanied by one or more of
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the following: diarrhea, abdominal cramps, bloating, flatulence, fatigue, and
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weight loss (see Table 1). Although vomiting and fever are listed in Table 1
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as relatively frequent symptoms, they have been uncommonly reported by people
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involved in waterborne outbreaks of giardiasis in the United States. Table 1
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also suggests that 13 percent of patients with giardiasis may have blood in
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their stool. Giardia, however, rarely causes intestinal bleeding. Therefore,
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blood in the stool of a patient with giardiasis almost always indicates the
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presence of a second disease.
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While most Giardia infections persist only for one or two months, some people
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undergo a more chronic phase, which can follow the acute phase or may become
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manifest without an antecedent acute illness. The chronic phase is
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characterized by loose stools, and increased abdominal gassiness with
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cramping, flatulence and burping. Fever is not common, but malaise, fatigue,
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and depression may ensue (2). For a small number of people, the persistence of
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infection is associated with the development of marked malabsorption and
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weight loss (3). Similarly, lactose (milk) intolerance can be a problem for
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some people. This can develop coincidentally with the infection or be
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aggravated by it, causing an increase in intestinal symptoms after ingestion
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of milk products.
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Some people may have several of these symptoms without evidence of diarrhea or
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have only sporadic episodes of diarrhea every 3 or 4 days. Still others may
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not have any symptoms at all. Therefore, the problem may not be whether you
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are infected with the parasite or not, but how harmoniously you both can live
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together, or how to get rid of the parasite (either spontaneously or by
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treatment) when the harmony does not exist or is lost.
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Medical Treatment
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Three drugs are available in the United States to treat giardiasis: quinacrine
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(Atabrine*), metronidazole (Flagyl*), and furazolidone (Furoxone*). All are
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prescription drugs. In a recent review of drug trials in which the efficacies
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of these drugs were compared, quinacrine produced a cure in 93% of 129
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patients, metronidazole cured 92% of 219, and furazolidone cured 84% of 150
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patients (4). Quinacrine is generally the least expensive of the anti-Giardia
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medications but it often causes vomiting in children younger than 5 years
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old. Although the treatment of giardiasis is not an FDA-approved indication
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for metronidazole, the drug is commonly used for this purpose. Furazolidone
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is the least effective of the three drugs, but is the only anti-Giardia
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medication that comes as a liquid preparation, which makes it easier to
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deliver the exact dose to small children and makes it the most convenient
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dosage form for children who have difficulty taking pills. Cases of chronic
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giardiasis refractory to repeated courses of therapy have been noted, one of
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which responded to combined quinacrine and metronidazole treatment (5).
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(*) Use of trade names is for purposes of identification only.
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Etiology and Epidemiology
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Giardiasis occurs worldwide. In the United States, Giardia is the parasite
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most commonly identified in stool specimens submitted to state laboratories
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for parasitologic examination. From 1977 through 1979, approximately 4% of 1
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million stool specimens submitted to state laboratories were positive for
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Giardia (6). Other surveys have demonstrated Giardia prevalence rates ranging
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from 1 to 20% depending on the location and ages of persons studied.
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Giardiasis ranks among the top 20 infectious diseases that cause the greatest
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morbidity in Africa, Asia, and Latin America (7); it has been estimated that
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about 2 million infections occur per year in these regions (8).
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People who are at highest risk for acquiring a Giardia infection in the United
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States may be placed into five major categories:
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1) People in cities whose drinking water originates from streams or
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rivers and whose water treatment process does not include
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filtration, or filtration is ineffective because of malfunctioning
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equipment.
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2) Hikers/campers/outdoorspeople.
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3) International travelers
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4) Children who attend day-care centers, day-care center staff, and
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parents and siblings of children infected in day-care centers.
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5) Homosexual men.
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People in categories 1, 2, and 3 have in common the same general source of
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infections, i.e., they acquire Giardia from fecally contaminated drinking
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water. The city resident usually becomes infected because the municipal water
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treatment process does not include a filter that is necessary to physically
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remove the parasite from the water. The number of people in the United States
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at risk (i.e., the number who receive municipal drinking water from unfiltered
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surface water) is estimated to be 20 million. International travelers may
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also acquire the parasite from improperly treated municipal waters in cities
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or villages in other parts of the world, particularly in developing
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countries. In Eurasia, only travelers to Leningrad appear to be at increased
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risk. In prospective studies, 88% of U.S. and 35% of Finnish travelers to
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Leningrad who had negative stool tests for Giardia on departure to the Soviet
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Union developed symptoms of giardiasis and had positive tests for Giardia
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after they returned home (10,11). With the exception of visitors to Leningrad,
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however, Giardia has not been implicated as a major cause of traveler's
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diarrhea. The parasite has been detected in fewer than 2% of travelers who
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develop diarrhea. Hikers and campers risk infection every time they drink
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untreated raw water from a stream or river.
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Persons in categories 4 and 5 become exposed through more direct contact with
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feces of an infected person, e.g., exposure to soiled diapers of an infected
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child (day-care center-associated cases), or through direct or indirect
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anal-oral sexual practices in the case of homosexual men.
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Although community waterborne outbreaks of giardiasis have received the
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greatest publicity in the United States during the past decade, about half of
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the Giardia cases discussed with staff of the Centers for Disease Control in
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the past 2 to 3 years have a day-care center exposure as the most likely
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source of infection. Numerous outbreaks of Giardia in day-care centers have
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been reported in recent years. Infection rates for children in day-care
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center outbreaks range from 21 to 44% in the United states and from 8 to 27%
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in Canada (12,13,14,15,16,17). The highest infection rates are usually
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observed in children who wear diapers (l to 3 years of age). In one study of
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18 randomly selected day care centers in Atlanta (CDC unpublished data), 10%
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of diapered children were found infected. Transmission from this age group to
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older children, day-care staff, and household contacts is also common. About
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20% of parents caring for an infected child will come infected.
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It is important that local health officials and managers of water utility
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companies realize that sources of Giardia infection other than municipal
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drinking water exist. Armed with this knowledge, they are less likely to make
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a quick (and sometimes wrong) assumption that a cluster of recently diagnosed
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cases in a city is related to municipal drinking water. Of course, drinking
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water must not be ruled out as a source of infection when a larger than
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expected number of cases are recognized in a community, but the possibility
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that the cases are associated with a day-care center outbreak, drinking
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untreated stream water, or international travel should also be
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entertained.
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Parasite Biology
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To understand the finer aspects of Giardia transmission and the strategies for
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control, one must become familiar with several aspects of the parasite's
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biology. Two forms of the parasite exist: a trophozoite and a cyst, both of
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which are much larger than bacteria (see Figure 1). Trophozoites live in the
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upper small intestine where they attach to the intestinal wall by means of a
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disc-shaped suction pad on their ventral surface. Trophozoites actively feed
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and reproduce at this location. At some time during the trophozoite's life,
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it releases its hold on the bowel wall and floats in the fecal stream through
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the intestine. As it makes this journey, it undergoes a morphologic
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transformation into an egglike structure called a cyst. The cyst, which is
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about 6 to 9 micrometers in diameter x 8 to 12 micrometers (1/100 millimeter)
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in length, has a thick exterior wall that protects the parasite against the
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harsh elements that it will encounter outside the body. This cyst form of the
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parasite is infectious for other people or animals. Most people become
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infected either directly by hand-to-mouth transfer of cysts from the feces of
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an infected individual, or indirectly by drinking feces-contaminated water.
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Less common modes of transmission included ingestion of fecally contaminated
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food and hand-to-mouth transfer of cysts after touching a fecally contaminated
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surface. After the cyst is swallowed, the trophozoite is liberated through
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the action of stomach acid and digestive enzymes and becomes established in
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the small intestine.
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Although infection after the ingestion of only one Giardia cyst is
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theoretically possible, the minimum number of cysts shown to infect a human
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under experimental conditions is ten (18). Trophozoites divide by binary
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fission about every 12 hours. What this means in practical terms that if a
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person swallowed only a single cyst, reproduction at this rate would result in
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more than 1 million parasites 10 days later, and 1 billion parasites by day 15.
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The exact mechanism by which Giardia causes illness is not yet well
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understood, but is not necessarily related to the number of organisms
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present. Nearly all of the symptoms, however, are related to dysfunction of
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the gastrointestinal tract. The parasite rarely invades other parts of the
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body, such as the gall bladder or pancreatic ducts. Intestinal infection does
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not result in permanent damage.
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Transmission
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Data reported to the CDC indicate that Giardia is the most frequently
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identified cause of diarrheal outbreaks associated with drinking water in the
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United States. The remainder of this article will be devoted to waterborne
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transmission of Giardia. Waterborne epidemics of giardiasis are a relatively
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frequent occurrence. In 1983, for example, Giardia was identified as the
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cause of diarrhea in 68% of waterborne outbreaks in which the causal agent was
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identified (19). From 1965 to 1982, more than 50 waterborne outbreaks were
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reported (20). In 1984, about 250,000 people in Pennsylvania were advised to
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boil drinking water for 6 months because of Giardia-contaminated water.
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Many of the municipal waterborne outbreaks of Giardia have been subjected to
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intense study to determine their cause. Several general conclusions can be
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made from data obtained in those studies. Waterborne transmission of Giardia
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in the United States usually occurs in mountainous regions where community
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drinking water is obtained from clear running streams, is chlorinated but is
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not filtered before distribution. Although mountain streams appear to be
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clean, fecal contamination upstream by human residents or visitors, as well as
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by Giardia-infected animals such as beavers, has been well documented. It is
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worth emphasizing that water obtained from deep wells is an unlikely source of
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Giardia because of the natural filtration of water as it percolates through
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the soil to reach underground cisterns. Well-water sources that pose the
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greatest risk of fecal contamination are those that are poorly constructed or
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improperly located. A few outbreaks have occurred in towns that included
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filtration in the water treatment process, but the filtration was not
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effective in removing Giardia cysts because of defects in filter construction,
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poor maintenance of the filter media, or inadequate pretreatment of the water
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before it was filtered. Occasional outbreaks have also occurred because of
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accidental cross-connections between water and sewerage systems.
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|
|
One can conclude from these data that two major ingredients are necessary for
|
|
waterborne outbreak. First, there must be Giardia cysts in untreated source
|
|
water and, second, the water purification process must either fail to kill or
|
|
fail to remove Giardia cysts from the water.
|
|
|
|
Although beavers are often blamed for contaminating water with Giardia cysts,
|
|
it seems unlikely that they are responsible for introducing the parasite into
|
|
new areas. It is far more likely that they are also victims: Giardia cysts
|
|
may be carried in untreated human sewage discharged into the water by
|
|
small-town sewage disposal plants or originate from cabin toilets that drain
|
|
directly into streams and rivers. Backpackers, campers, and sports
|
|
enthusiasts may also deposit Giardia-contaminated feces in the environment
|
|
that are subsequently washed into streams by rain. In support of this concept
|
|
is a growing amount of data that indicate a higher Giardia infection rate in
|
|
beavers living downstream from U.S. National Forest campgrounds compared with
|
|
a near zero rate of infection in beavers living in more remote areas.
|
|
|
|
Although beavers may be unwitting victims in the Giardia story, they still
|
|
play an important part in the transmission scheme, because they can (and
|
|
probably do) serve as amplifying hosts. An amplifying host is one that is
|
|
easy to infect, serves as a good habitat for the parasite to reproduce, and,
|
|
in the case of Giardia, returns millions of cysts to the water for every one
|
|
ingested. Beavers are especially important in this regard because they tend
|
|
to defecate in or very near the water, which ensures that most of the Giardia
|
|
cysts excreted are returned to the water
|
|
|
|
The contribution of other animals to waterborne outbreaks of Giardia is less
|
|
clear. Muskrats (another semiaquatic animal) have been found in several parts
|
|
of the United States to have high infection rates (30 to 40%) (2l). Recent
|
|
studies have shown that muskrats can be infected with Giardia cysts obtained
|
|
from humans and beavers. Occasional Giardia infections have been reported in
|
|
coyotes, deer, elk, cattle, dogs, and cats, but not in horses and sheep,
|
|
encountered in mountainous regions of the United States. Naturally occurring
|
|
Giardia infections have not been found in most other wild animals (bear,
|
|
nutria, rabbit, squirrel, badger, marmot, skunk, ferret, porcupine, mink,
|
|
raccoon, river otter, bobcat, lynx, moose, bighorn sheep) (22).
|
|
|
|
Removal from Municipal Water Supplies
|
|
|
|
During the past 10 years, scientific knowledge about what is required to kill
|
|
or remove Giardia cysts from a contaminated water supply has increased
|
|
considerably. For example, it is known that cysts can survive in cold water
|
|
(4 deg C) for at least 2 months and that they are killed instantaneously by
|
|
boiling water (100 deg C) (23,24). It is not known how long the cysts
|
|
will remain viable at other water temperatures (e.g., at 0 deg C or in a
|
|
canteen at 15-20 deg C), nor is it known how long the parasite will survive
|
|
on various environment surfaces, e.g., under a pine tree, in the sun,
|
|
on a diaper-changing table, or in carpets in a day-care center.
|
|
|
|
The effect of chemical disinfection, such as chlorine, on the viability of
|
|
Giardia cysts is an even more complex issue. It is clear from the number of
|
|
waterborne outbreaks of Giardia that have occurred in communities where
|
|
chlorine was employed as a disinfectant that the amount of chlorine used
|
|
routinely for municipal water treatment is not effective against Giardia
|
|
cysts. These observations have been confirmed in the laboratory under
|
|
experimental conditions (25,26,27). This does not mean, however, that chlorine
|
|
does not work at all. It does work under certain favorable conditions.
|
|
Without getting too technical, one can gain some appreciation of the problem
|
|
by understanding a few of the variables that influence the efficacy of
|
|
chlorine as a disinfectant.
|
|
|
|
1) Water pH: at pH values above 7.5, the disinfectant capability of
|
|
chlorine is greatly reduced.
|
|
2) Water temperature: the warmer the water, the higher the efficacy.
|
|
Thus, chlorine does not work well in ice-cold water from mountain
|
|
streams.
|
|
3) Organic content of the water: mud, decayed vegetation, or other
|
|
suspended organic debris in water chemically combines with chlorine
|
|
making it unavailable as a disinfectant.
|
|
4) Chlorine contact time: the longer Giardia cysts are exposed to
|
|
chlorine, the more likely it is that the chemical will kill them.
|
|
5) Chlorine concentration: the higher the chlorine concentration, the
|
|
more likely chlorine will kill Giardia cysts. Most water treatment
|
|
facilities try to add enough chlorine to give a free (unbound)
|
|
chlorine residual at the customer tap of 0.5 mg per liter of water.
|
|
|
|
The five variables above are so closely interrelated that an unfavorable
|
|
occurrence in one can often be compensated for by improving another. For
|
|
example, if chlorine efficacy is expected to be low because water is obtained
|
|
from an icy stream, either the chlorine contact time or chlorine
|
|
concentration, or both could be increased. In the case of
|
|
Giardia-contaminated water, it might be possible to produce safe drinking
|
|
water with a chlorine concentration of 1 mg per liter and a contact time as
|
|
short as 10 minutes if all the other variables were optimal (i.e., pH of 7.0,
|
|
water temperature of 25 deg C, and a total organic content of the water close to
|
|
zero). On the other hand, if all of these variables were unfavorable (i.e.,
|
|
pH of 7.9, water temperature of 5 deg C, and high organic content), chlorine
|
|
concentrations in excess of 8 mg per liter with several hours of contact time
|
|
may not be consistently effective. Because water conditions and water
|
|
treatment plant operations (especially those related to water retention time
|
|
and, therefore, to chlorine contact time) vary considerably in different parts
|
|
of the United States, neither the U.S. Environmental Protection Agency nor the
|
|
CDC has been able to identify a chlorine concentration that would be safe yet
|
|
effective against Giardia cysts under all water conditions. Therefore, the
|
|
use of chlorine as a preventive measure against waterborne giardiasis
|
|
generally has been used under outbreak conditions when the amount of chlorine
|
|
and contact time have been tailored to fit specific water conditions and the
|
|
existing operational design of the water utility.
|
|
|
|
In an outbreak, for example, the local health department and water utility may
|
|
issue an advisory to boil water, may increase the chlorine residual at the
|
|
consumer's tap from 0.5 mg per liter to 1 or 2 mg per liter, and, if the
|
|
physical layout and operation of the water treatment facility permit, increase
|
|
the chlorine contact time. These are emergency procedures intended to reduce
|
|
the risk of transmission until a filtration device can be installed or
|
|
repaired or until an alternative source of safe water, such as a well, can be
|
|
made operational.
|
|
|
|
The long-term solution to the problem of municipal waterborne outbreaks of
|
|
giardiasis will involve improvements in and more widespread use of filters in
|
|
the municipal water treatment process. The sand filters most commonly used in
|
|
municipal water treatment today cost millions of dollars to install, which
|
|
makes them unattractive for many small communities. Moreover, the pore sizes
|
|
in these filters are not sufficiently small to remove a Giardia (6 to 9
|
|
micrometers x 8 to 12 micrometers). For the sand filter to remove Giardia
|
|
cysts from the water effectively, the water must receive some additional
|
|
treatment before it reaches the filter. In addition, the flow of water
|
|
through the filter bed must be carefully regulated.
|
|
|
|
An ideal prefilter treatment for muddy water would include sedimentation (a
|
|
holding pond where the large suspended particles are allowed to settle out by
|
|
the action of gravity) followed by flocculation or coagulation (the addition
|
|
of chemicals such as alum or ammonium to cause microscopic particles to clump
|
|
together). The large particles resulting from the flocculation/coagulation
|
|
process, including Giardia cysts bound to other microparticulates, are easily
|
|
removed by the sand filter. Chlorine is then added to kill the bacteria and
|
|
viruses that may escape the filtration process. If the water comes from a
|
|
relatively clear source, chlorine may be added to the water before it reaches
|
|
the filter. The point here is that successful operation of a complete water
|
|
treatment facility is a complex process that requires considerable training.
|
|
Troubleshooting breakdowns or recognizing potential problems in the system
|
|
before they occur often requires the skills of an engineer. Unfortunately,
|
|
most small water utilities that have a water treatment facility that includes
|
|
filtration cannot afford the services of a full-time engineer. Filter
|
|
operation or maintenance problems in such systems may not be detected until a
|
|
Giardia outbreak is recognized in the community. The bottom line is that
|
|
although, in reference to municipal systems, water filtration is the best that
|
|
water treatment technology has to offer against waterborne giardiasis, it is
|
|
not infallible. For municipal water filtration facilities to work properly,
|
|
they must be properly constructed, operated, and maintained.
|
|
|
|
Water Disinfection in the Out-of-Doors
|
|
|
|
Whenever possible, persons in the out-of-doors should carry drinking water of
|
|
known purity with them. When this is not practical, and water from streams,
|
|
lakes, ponds, and other outdoor sources must be used, time should be taken to
|
|
disinfect the water before drinking it.
|
|
|
|
Boiling
|
|
|
|
Boiling water is one of the simplest and most effective ways to purify water.
|
|
Boiling for 1 minute is adequate to kill Giardia as well as most other
|
|
bacterial or viral pathogens likely to be acquired from drinking polluted
|
|
water.
|
|
|
|
Chemical Disinfection
|
|
|
|
Disinfection of water with chlorine or iodine is considered less reliable than
|
|
boiling for killing Giardia. However, it is recognized that boiling drinking
|
|
water is not practical under many circumstances. Therefore, when one cannot
|
|
boil drinking water, chemical disinfectants such as iodine or chlorine should
|
|
be used. This will provide some protection against Giardia and will destroy
|
|
most bacteria and viruses that cause illness. Iodine or chlorine concentrations
|
|
of 8 mg/liter (8ppm) with a minimum contact time of 30 minutes are recommended.
|
|
If the water is cold (less than 10 deg C or 5O deg F) we suggest a minimum
|
|
contact time of 60 minutes. If you have a choice of disinfectants, use iodine.
|
|
Iodine's disinfectant activity is less likely to be reduced by unfavorable
|
|
water conditions, such as dissolved organic material in water or by water with
|
|
a high pH, than chlorine.
|
|
|
|
Below are instructions for disinfecting water using household tincture of
|
|
iodine or chlorine bleach. If water is visibly dirty, it should first be
|
|
strained through a clean cloth into a container to remove any sediment or
|
|
floating matter. Then the water should be treated with chemicals as follows:
|
|
|
|
IODINE
|
|
|
|
Tincture of iodine from the medicine chest or first aid kit can be used to
|
|
treat water. Mix thoroughly by stirring or shaking water in container and let
|
|
stand for 30 minutes.
|
|
|
|
Tincture of Iodine Drops* to be Added per Quart or Liter
|
|
Clear Water Cold or Cloudy Water**
|
|
|
|
2% 5 10
|
|
|
|
* 1 drop = 0.05ml
|
|
|
|
** Very turbid or very cold water may require prolonged contact time; let
|
|
stand up to several hours or even overnight.
|
|
|
|
CHLORINE
|
|
|
|
Liquid chlorine bleach used for washing clothes usually has 4% to 6% available
|
|
chlorine. The label should be read to find the percentage of chlorine in the
|
|
solution and the treatment schedule below should be followed.
|
|
|
|
Drops* to be Added per Quart or Liter
|
|
Available Chlorine Clear Water Cold or Cloudy Water**
|
|
|
|
1% 10 20
|
|
4% to 6% 2 4
|
|
7% to lO% 1 2
|
|
Unknown 10 20
|
|
|
|
* 1 drop = 0.05ml
|
|
|
|
** Very turbid or very cold water may require prolonged contact time; let
|
|
stand up to several hours or even overnight.
|
|
|
|
|
|
Mix thoroughly by stirring or shaking water in container and let stand for 30
|
|
minutes. A slight chlorine odor should be detectable in the water; if not,
|
|
repeat the dosage and let stand for an additional 15 minutes before using.
|
|
|
|
Filters
|
|
|
|
Newcomers in the battle against waterborne giardiasis include a variety
|
|
of portable filters for field or individual use as well as some household
|
|
filters. Manufacturers' data accompanying these filters indicate that some
|
|
can remove particles the size of a Giardia cyst or smaller and may be capable
|
|
of providing a source of safe drinking water for an individual or family
|
|
during a waterborne outbreak. Such devices, if carefully selected, might also
|
|
be useful in preventing giardiasis in international travelers, backpackers,
|
|
campers, sportsmen, or persons who live or work in areas where water is known
|
|
to be contaminated.
|
|
|
|
Unfortunately, there are yet few published reports in the scientific
|
|
literature detailing both the methods used and the results of tests employed
|
|
to evaluate the efficacy of these filters against Giardia. Until more
|
|
published experimental data become available, there are a few common sense
|
|
things that a consumer should look for when selecting a portable or household
|
|
filter. The first thing to consider is the filter media. Filters relying
|
|
solely on ordinary or silver-impregnated carbon or charcoal should be avoided,
|
|
because they are not intended to prevent, destroy, or repel micro-organisms.
|
|
Their principal use is to remove undesirable chemicals, odors, and very large
|
|
particles such as rust or dirt.
|
|
|
|
Some filters rely on chemicals such as iodide-impregnated resins to kill
|
|
Giardia. While properly designed and manufactured iodide-impregnated resin
|
|
filters have been shown to kill many species of bacteria and virus present in
|
|
human feces, their efficacy against Giardia cysts is less well-established.
|
|
The principle under which these filters operate is similar to that achieved by
|
|
adding the chemical disinfectant iodine to water, except that the
|
|
micro-organisms in the water pass over the iodide-impregnated disinfectant as
|
|
the water flows through the filter.
|
|
|
|
While the disinfectant activity of iodide is not as readily affected as
|
|
chlorine by water pH or organic content, iodide disinfectant activity is
|
|
markedly reduced by cold water temperatures. Experiments on Giardia indicate
|
|
that many of the cysts in cold water (4 deg C) remain viable after passage
|
|
through filters containing tri-iodide or penta-iodide disinfectants (28). As
|
|
indicated earlier, longer contact times (compared to those required to kill
|
|
bacteria) are required when using chemical filters to process cold water for
|
|
Giardia protection. Presently available chemical filters also are not
|
|
recommended for muddy or very turbid water. Additionally, filters relying
|
|
solely on chemical action usually give no indication to the user when
|
|
disinfectant activity has been depleted.
|
|
|
|
The so-called microstrainer types of filters are true filters. Manufacturer
|
|
data accompanying these filters indicate that some have a sufficiently small
|
|
pore size to physically restrict the passage of some micro-organisms through
|
|
the filter. The types of filter media employed in microstraining filters
|
|
include orlon, ceramic, and proprietary materials. Theoretically, a filter
|
|
having an absolute pore size of less than 6 micrometers might be able to
|
|
prevent Giardia cysts of 8 to 10 micrometers in diameter from passing.
|
|
However, when used as a water sampling device during community outbreaks,
|
|
portable filters in the 1- to 3- micrometer range more effectively removed
|
|
Giardia cysts from raw water than filters with larger pore sizes. For
|
|
effective removal of bacterial or viral organisms which cause disease in
|
|
humans, microstraining filters with pore sizes of less than 1 micrometer are
|
|
advisable. However, the smaller the pores, the more quickly the filters will
|
|
tend to clog. To obtain maximum filter life, and as a matter of reasonable
|
|
precaution, the cleanest available water source should always be used. Keep
|
|
in mind, however, that even sparkling, clear mountain streams can be heavily
|
|
contaminated.
|
|
|
|
Secondly, because infectious organisms can be concentrated on the filter
|
|
element/media, it is important to consider whether the filter element can be
|
|
cleaned or replaced without posing a significant health hazard to the user.
|
|
Properly engineered portable filters should also minimize the possibility of
|
|
contaminating the "clean water side" of the filter with contaminated water
|
|
during replacement or cleaning of the filter element. This is especially
|
|
important for filters used in the field where they are often rinsed or
|
|
"cleaned" in a stream or river that may be contaminated.
|
|
|
|
Ongerth (29) recently evaluated four filters (First Need, H20K, Katadyn, the
|
|
Pockett Purifier) for their ability to remove Giardia cysts from water. Only
|
|
the First Need and Katadyn filters removed 100% of the cysts.
|
|
|
|
Conclusion
|
|
|
|
In conclusion, during the past fifteen years, giardiasis has been recognized
|
|
as one of the most frequently occurring waterborne diseases in the United
|
|
States. The most common sources of water contamination include improperly
|
|
treated municipal sewage, infected animals, and indiscriminate defecation by
|
|
outdoorsmen. Chlorine concentrations in the 0.1 mg per liter to 0.5 mg per
|
|
liter range are largely ineffective against Giardia at the contact times
|
|
commonly employed by municipal water utilities. The long-term solution to the
|
|
problem of municipal waterborne outbreaks of giardiasis will involve
|
|
appropriate pretreatment combined with improvements in and more widespread use
|
|
of filters in the municipal water treatment process. While both micrometer-
|
|
and submicrometer-rated filters are being employed on a limited scale for
|
|
personal or household use, further evaluation of the efficacy of filters
|
|
distributed by different manufacturers is needed to enable individuals and
|
|
public health personnel to distinguish those that are safe and effective from
|
|
those that are not.
|
|
|
|
TABLE I
|
|
Percentage Number
|
|
of Patients
|
|
|
|
Symptoms
|
|
|
|
Diarrhea* 84 516
|
|
Malaise 80 56
|
|
Weakness 72 324
|
|
Abdominal cramps 63 412
|
|
Weight loss (O.5 - 11 kg) 63 412
|
|
Greasy, foul smelling stools 59 412
|
|
Nausea 57 444
|
|
Headaches 53 92
|
|
Anorexia 49 156
|
|
Abdominal bloating 45 380
|
|
Flatulence 41 388
|
|
Constipation 25 88
|
|
Vomiting 24 488
|
|
Fever 22 32
|
|
|
|
Physical finding
|
|
|
|
Abdomen tender to palpitation 66 92
|
|
|
|
Laboratory findings
|
|
Blood
|
|
Anemia 15 124
|
|
Leukocytosis 9 32
|
|
|
|
Stool
|
|
Increased mucus 56 32
|
|
Increased neutral fats 50 32
|
|
Blood 13 156
|
|
|
|
* Index symptom; may be biased (upward)
|
|
|
|
|
|
|
|
|
|
TABLE 1 - Based on data from Fifty diseases: Fifty Diagnoses, by M.G. Periroth
|
|
and D.J. Weiland.
|
|
Year Book Medical Publishers, Inc., Chicago, 1981, pp. 158-159. Reprinted by
|
|
special arrangement with Year Book Publishers, Inc.
|
|
|
|
References
|
|
|
|
1. Craun, Gunther T. Waterborne Giardiasis in the United States: A review.
|
|
American Journal of Public Health 69:817-819, 1979.
|
|
|
|
2. Weller, Peter F. Intestinal Protozoa: Giardiasis. Scientific American
|
|
Medicine, 1985
|
|
|
|
3. Id. 2.
|
|
|
|
4. Davidson, R.A. Issues in Clinical Parasitology: The treatment of Giardiasis.
|
|
Am J. Gastroenterol. 79:256-261, 2984
|
|
|
|
5. Id. 2.
|
|
|
|
6. Intestinal Parasite Surveillance, Annual Summary 1978, Atlanta, Centers for
|
|
Disease Control, 1979.
|
|
|
|
7. Walsh, J.D. Warren K. s. Selective Primary Health Care: An Interim Strategy
|
|
for Disease Control in developing countries. N. Engl. J. Med., 301:967-974,
|
|
1979.
|
|
|
|
8. Walsh, J.A. Estimating the Burden of Illness in the Tropics, In Tropical and
|
|
Geographic Medicine, Edited by K.S. Warren and A.F. Mahmoud, McGraw-Hill,
|
|
New York, 1981, pp 1073-1085.
|
|
|
|
9. Weniger, B.D., Blaser, MlJ., Gedrose, J., Lippy, E.C., Juranek, D.D. an
|
|
Outbreak of Waterborne Giardiasis Associated with Heavy Water Runoff due to
|
|
Warm Weather and Volcanic Ashfall. Am. J. Public Health 78:868-872, 1983.
|
|
|
|
10. Brodsky, R.E., Spencer, H.C., Schultz, M.G. Giardiasis in American
|
|
Travelers to the Soviet Union. J. Infect Dis. 130:319-323, 1974.
|
|
|
|
11. Jokipii, L., Jokipii, A.M.M. Giardiasis in Travelers: A prospective Study.
|
|
J. Infect. Dis., 130:295-299, 1974.
|
|
|
|
12. Black, R.E., Dykes, A.C., Anderson, K.E., Wells, J.G., Sinclair, S.P.,
|
|
Gary, G.W., Hatch, M.H., Gnagarosa, E.J. Handwashing to Prevent Diarrhea in
|
|
Day-Care Centers. Am. J. Epidemiol. 113:445-451, 1981.
|
|
|
|
13. Pickering, L.K., Woodward, W.E., DuPont, H. L., Sullivan, P. Occurrence of
|
|
Giardia lamblia in Children in Day Care Centers. J. Pediatr. 104:522-526,
|
|
1984.
|
|
|
|
14. Sealy, D.P., Schuman, S.H. Endemic Giardiasis and Day Care. Pediatrics
|
|
72:154-158, 1983.
|
|
|
|
15. Pickering, L.K., Evans, D.G., DuPont, H.L., Vollet, J.J., III, Evans, D.J.,
|
|
Jr. diarrhea Caused by Shigella, Rotavirus, and Giardia in Day-care
|
|
Centers: Prospective Study. J. Peidatr., 99:51-56, 1981.
|
|
|
|
16. Keystone, J.S., Yang, J., Grisdale, D., Harrington, M., Pillow, L.,
|
|
Andreychuk, R. Intestinal Parasites in Metropolitan Toronto Day-Care
|
|
Centres. Can J. Assoc. J. 131:733-735, 1984.
|
|
|
|
17. Keystone, J.S., Kraden, S., Warren, M.R. Person-to-Person Transmission of
|
|
Giardia lamblia in Day-Care Nurseries. Can. Med. Assoc. J. 119:241-242,
|
|
247-248, 1978.
|
|
|
|
18. Rendtorff, R.C. The Experimental Transmission of Human Intestinal Protozoan
|
|
Parasites. II. Giardia lamblia cysts Given In Capsules, Am. J. Hygiene
|
|
59:209-220, 1954.
|
|
|
|
19. Water-related Disease Outbreaks Surveillance, Annual Summary 1983. Atlanta,
|
|
Centers for Disease Control, 1984.
|
|
|
|
20. Craun, G.F. Waterborne Outbreaks of Giardiasis--Current Status in Giardia
|
|
and Giardiasis, edited by S.L. Erlandsen and E.A Meyer. Pleunu Press. New
|
|
York, 1984, pp 243-261.
|
|
|
|
21. Frost, F. Plan, B., Liechty, B. Giardia Prevalence in Commercially Trapped
|
|
Mammals. J. Environ. Health 42:245-249.
|
|
|
|
22. Id. 21.
|
|
|
|
23. Id. 18.
|
|
|
|
24. Bingham, A.K., Jarroll, E.L., Meyer, E.A. Radulescu, S. Introduction of
|
|
Giardia Excystation and the effect of Temperature on cyst Viability
|
|
compared by Eosin-Exclusion and In Vitro Excystation in Waterborne
|
|
Transmission of Giardiasis. Edited by J. Jakubowski and H. C. Hoff, U.S.
|
|
Environmental Protection Agency, Washington, DC, 1979, pp. 217-229.
|
|
EPA-600/9-79-001.
|
|
|
|
25. Jarroll, E.L., Bingham, A.K., Meyer, E.A. Effect of Chlorine on Giardia
|
|
lamblia Cyst Viability. Appl. Environ. Microbiol. 41:483-487, 1981.
|
|
|
|
26. Jarroll, E.L., Jr., Bingham, A.K. Meyer, E.A. Inability of an Iodination
|
|
Method to Destroy completely Giardia Cysts in Cold Water. West J. Med.
|
|
132:567-569, 1980.
|
|
|
|
27. Jarroll, E.L., Jr., Bingham, A.K., Meyer, E.A. Giardia Cyst Destruction:
|
|
Effectiveness of Six Small-Quantity Water Disinfection Methods. Am. J.
|
|
Trop. Med. Hygiene 29:8-11, 1980.
|
|
|
|
28. Marchin, B.L., Fina, L.R., Lambert, J.L., Fina, G.T. Effect of resin
|
|
disinfectants--13 and --15 on Giardia muris and giardia lamblia. Appl
|
|
Environ. Microbiol. 46:965-9, 1983.
|
|
|
|
29. Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country
|
|
water treatment to prevent giardiasis. Am J Public Health
|
|
1989;79(12):1633-7.
|
|
|
|
=====
|
|
|
|
Back-country water treatment to prevent giardiasis.
|
|
Jerry E. Ongerth, PhD, PE, Ron L. Johnson, Steven C Macdonald, MPH, Floyd Frost,
|
|
PhD, and Henry H. Stibbs, PhD
|
|
|
|
American Journal of Public Health December 1989, Vol 79, No 12, pp 1633-1637.
|
|
|
|
Copyright 1989 AJPH 0090-0036/89$1.50 [used without permission]
|
|
|
|
Abstract
|
|
|
|
This study was conducted to provide current information on the effectiveness of
|
|
water treatment chemicals and filters for control of Giardia cysts in areas
|
|
where treated water is not available. Four filters and seven chemical
|
|
treatments were evaluated for both clear and turbid water at 10C. Three contact
|
|
disinfection devices were also tested for cyst inactivation. Filters were
|
|
tested with 1-liter volumes of water seeded with 3x10^4 cysts of G. lamblia
|
|
produced in gerbils inoculated with in vitro cultured trophozoites; the entire
|
|
volume of filtrate was examined for cyst passage. Chemical treatments were
|
|
evaluated at concentrations specified by the manufacturer and for contact times
|
|
that might be expected of hikers (30 minutes) and campers (eight hours, i.e.,
|
|
overnight). Two of the four filter devices tested were 100 percent effective
|
|
for Giardia cyst removal. Of the other two filters, one was 90 percent
|
|
effective and the other considerably less effective. Among the seven
|
|
disinfection treatments, the iodine-based chemicals were all significantly more
|
|
effective than the chlorine-based chemicals. None of the chemical treatments
|
|
achieved 99.9 percent cyst inactivation with only 30-minute contact. After an
|
|
eight-hour contact each of the iodine but none of the chlorine preparations
|
|
achieved at least 99.9 percent cyst inactivation. None of the contact
|
|
disinfection devices provided appreciable cyst inactivation. Heating water to
|
|
at least 70C for 10 minutes was an acceptable alternative treatment.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Introduction
|
|
|
|
Giardia lamblia is the most commonly identified human intestinal parasite in the
|
|
United States. Giardiasis is commonly transmitted between humans, especially
|
|
among small children. lt is also transmitted in water, particularly in the
|
|
mountainous regions of the U.S. Since 1965, over 80 waterborne outbreaks of
|
|
giardiasis have occurred in community water systems, affecting more than 20,000
|
|
persons (1). Giardiasis in hikers and campers has also been documented (2,3);
|
|
indeed, it is commonly considered a backpackers' illness. Giardia cysts in
|
|
concentrations as high as four per gallon have been detected in untreated
|
|
surface water in northeastern and western states (4).
|
|
|
|
Concern over waterborne transmission of Giardia has led to development of a
|
|
variety of chemical disinfectants and portable filters for individual use in the
|
|
backcountry. Although some information on such methods has been reported
|
|
(2,5,6), there is no comprehensive guide to their reliability in actually
|
|
removing or inactivating Giardia cysts. We tested four commercially available
|
|
portable filters and one contact disinfection device for their ability to remove
|
|
Giardia cysts from water. We also evaluated the cysticidal effectiveness of
|
|
seven chemical disinfectants and three contact disinfection devices.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Methods
|
|
|
|
Cysts of G. lamblia were prepared for use in both the filtration and
|
|
disinfection tests by propagation in gerbils inoculated with trophozoites from
|
|
sterile culture. Trophozoites were of two isolates: one from a beaver (Be-4
|
|
isolate from Alberta) and one from a human (H-2 CSU isolate from Colorado).
|
|
Cysts were concentrated from crushed, filtered gerbil feces by flotation on zinc
|
|
sulfate (sp. gr. 1.18), cleaned, and stored in distilled water at 4C for up to
|
|
10 days before use. Similarly, G. muris cysts of an isolate originally obtained
|
|
from hamsters (7) were purified from feces of infected athymic (nu/nu) mice and
|
|
stored before use. Cyst concentrations were determined with a Coulter Counter
|
|
(Model ZBI, Coulter Electronics, Hialeah, FL) and a haemacytometer. Except
|
|
where noted, cysts were added to water samples in concentrations of about
|
|
3x10^4/ml. Cyst viability was assayed by fluorogenic staining (8) and in vitro
|
|
excystation (7). In the former method, live cysts are distinguished by two
|
|
fluorescing dyes. One dye is fluorescein diacetate (FDA), which when absorbed
|
|
by cysts produces a fluorescent green only in live cysts; the second dye, either
|
|
propidium iodide (Pl) or ethidium bromide (EB), is excluded efficiently by live
|
|
cysts but absorbed by dead cysts, resulting in red fluorescence.
|
|
|
|
Filter testing
|
|
|
|
The following backpacker-type water filters were purchased from local retailers:
|
|
First Need Water Purification Device (First Need), General Ecology Inc.,
|
|
Lionville, PA; H2OK Portable Drinking Water Treatment Unit Model No. 6 (H2OK),
|
|
Better Living Laboratories Inc., Memphis, TN; Katadyn Pocket Filter (Katadyn),
|
|
Katadyn Products Inc., Wallisellen, Switzerland; and Pocket Purifier, Calco Ltd,
|
|
Rosemont, IL. Also noted in this category is the Water Tech Water Purifier
|
|
(Water Purifier), Water Technologies Corp., Ann Arbor, Ml. Although it is not
|
|
advertised as a filter and was not specifically tested for Giardia cyst removal,
|
|
we report qualitative observations made during disinfection testing (see below)
|
|
because its configuration and mode of operation suggest that particle removal
|
|
may occur. Physical and operating information provided in the filter packaging
|
|
is summarized in Appendix A. Each device was tested when it was new. Devices
|
|
that removed all cysts when new were retested after a period of use
|
|
approximating several months for a regular weekend user.
|
|
|
|
Each filter was prepared for testing by filtering four liters of tap water to
|
|
purge loose carbon particles or debris. The cyst removal performance of each
|
|
filter was determined by filtering one liter of spring water, turbidity of 0.1
|
|
NTU, to which formalin-fixed G. lamblia cysts had been added. The entire
|
|
filtrate volume was passed through a 25-mm dia., 5-um pore size, polycarbonate
|
|
membrane (Nuclepore, Pleasanton, CA). stained with EB (100 ug/ml), and mounted
|
|
under a cover slip. Cysts were counted at x250 magnification with the aid of
|
|
epifluorescence microscopy. A representative portion of each filter was
|
|
examined to quantify cyst recovery as described previously (9). The area
|
|
examined was inversely proportional to the number of cysts found and ranged from
|
|
3.5 percent of seeded positive control filters to 25 percent (one quadrant) of
|
|
filters with cyst densities less than one per field. Total numbers of cysts
|
|
present were estimated by extrapolation in direct proportion to the area
|
|
examined. In extensive work on recovery of Giardia cysts using the procedures
|
|
described above, cyst retention on the 5-um polycarbonate membrane in a single
|
|
filtration step has routinely averaged 80 to 90 percent (Ongerth JE:
|
|
unpublished). Accordingly, the ability to identify high levels of cyst removal,
|
|
which would result in passage of very few or no cysts, is excellent. This
|
|
ability is unaffected by the factors that contribute to lack of precision in
|
|
counting large numbers of cysts on filters; such inaccuracies usually occur when
|
|
only small representative subareas are examined and the total numbers are
|
|
estimated by extrapolation. A seeded positive control and an unseeded negative
|
|
control were processed with each batch of filter evaluations. The cyst removal
|
|
performance evaluation was replicated three times for each filter device, with
|
|
results expressed as the arithmetic average and corresponding standard
|
|
deviation.
|
|
|
|
Contact Disinfection Testing
|
|
|
|
The Water Purifier is described in packaging information as a contact
|
|
disinfection device. Likewise, the H2OK and Pocket Purifier devices are
|
|
described as providing disinfection as well as removing cysts by filtration.
|
|
These devices were therefore tested for their effect on cyst viability in
|
|
addition to filtration efficiency. A single 500-ml sample for each device was
|
|
seeded with approximately 2.5 x 10^4 cysts and passed through the device.
|
|
Filtrate was collected and filtered as described above to recover cysts. The
|
|
viability of cysts was then assessed by FDA and EB staining as described below.
|
|
|
|
Disinfectant Testing
|
|
|
|
The cysticidal effects of seven commercially available and commonly used
|
|
disinfectant preparations were tested with identical procedures. Four of the
|
|
products were iodine based: Polar Pure Water Disinfectant (Polar Pure), Polar
|
|
Equipment, Saratoga, CA; Coghlan's Emergency Germicidal Drinking Water Tablets
|
|
(CEGDWT). Coghlan's Ltd, Winnipeg. Canada; Potable Aqua Drinking Water
|
|
Germicidal Tablets (Potable Aqua), Wisconsin Pharmacal Inc., Jackson, WI; and 2
|
|
percent iodine prepared from I2 reagent grade (Baker, Phillipsburg, NJ). The
|
|
remaining three products were chlorine-based: Sierra Water Purifier (Sierra), 4
|
|
in 1 Water Co., Santa Fe, NM; Halazone, Abbott Laboratories, North Chicago, IL;
|
|
and commercial liquid bleach (5.25 percent sodium hypochlorite). Disinfectant
|
|
solutions were characterized by pH and total halogen concentration (Appendix B),
|
|
the latter being determined colorimetrically using the DPD method.
|
|
|
|
Two water sources were used, one to reflect clear high-mountain conditions, the
|
|
other to reflect downstream, more turbid conditions. Water sources were
|
|
characterized by pH, turbidity, and free chlorine demand (Appendix C). The
|
|
upstream source was from a small, spring-fed tributary to the Snoqualmie River
|
|
near North Bend, Washington. Samples were taken from the stream approximately
|
|
50 yards downstream from the spring. The downstream source was the discharge
|
|
from Lake Washington in Seattle, Washington. Samples were taken in midstream at
|
|
the entrance to Portage Bay, adjacent to the University of Washington campus.
|
|
Water samples were prepared for testing by adding disinfectant, according to
|
|
manufacturers' instructions, to one liter of water in stoppered glass bottles
|
|
(Appendix B).
|
|
|
|
Cysticidal properties of the chemical treatments were determined as follows.
|
|
|
|
1) Water was put in 50-ml disposable plastic centrifuge tubes and placed in a
|
|
10C incubator.
|
|
|
|
2) G. lamblia cysts were added to each test sample at time zero.
|
|
|
|
3) Tubes were vortex-mixed, sampled, and returned to the incubator.
|
|
|
|
4) At each sampling time, i.e., time 0, 30 minutes and 8 hours, a 10-ml sample
|
|
was withdrawn; a portion was used for measuring disinfectant concentration, and
|
|
in the remainder the disinfectant was quenched with 0.1-mM sodium thiosulphate.
|
|
|
|
5) Cysts in the quenched sample portion were exposed to aqueous solutions of the
|
|
viability indicators, FDA (25 ug/ml) and EH (100 ug/ml), filtered on to a 13-mm
|
|
dia. 5-um pore-size filter membrane, and rinsed with distilled water (10 ml).
|
|
|
|
6) Filters were mounted on glass slides, sealed under coverslips and examined by
|
|
epifluorescence microscopy at x250 magnification (Model 16, Carl Zeiss, Inc.,
|
|
Thornwood, NY) to enumerate proportions of red and green fluorescing cysts
|
|
indicating dead and live status, respectively. The viability baseline of the
|
|
cysts was established by running a control sample of untreated water seeded with
|
|
cysts through each test, using procedures identical to those for disinfectant-
|
|
treated samples. Data are presented in terms of percent survival relative to
|
|
the controls (Figure 2). The effectiveness of each disinfectant for killing
|
|
cysts in both upstream and downstream water was determined in triplicate, with
|
|
results expressed as the arithmetic average and corresponding standard
|
|
deviation.
|
|
|
|
The Water Tech Water Purifier, a contact disinfectant, was also tested as a
|
|
chemical disinfectant. The test water was 100 ml of spring-source water seeded
|
|
with Giardia cysts. The treated water was filtered, stained, and examined for
|
|
cyst viability as described in steps 5 and 6 above. Three replicates were
|
|
assayed.
|
|
|
|
Heat Inactivation
|
|
|
|
Inactivation of G. lamblia and G. muris cysts by heating was established as
|
|
follows. Cysts were added to distilled water in 15-ml glass test tubes. The
|
|
seeded tubes were incubated for 10 minutes at temperatures ranging from 10C to
|
|
70C. Afterwards, cyst suspensions were cooled immediately by swirling in 10C
|
|
water for one minute. Cyst viability was determined either by excystation or by
|
|
staining. If by the latter, FDA and EB were added to the samples, the tubes
|
|
were vortex-mixed, and a 1-ml aliquot was filtered through a 13-mm dia. 5-um
|
|
pore-size filter membrane. Filters were rinsed, mounted, and examined as
|
|
described above to enumerate the live and dead cysts.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Results
|
|
|
|
Filter Device Tests
|
|
|
|
The four filters differed significantly in their ability to remove Giardia cysts
|
|
(Figure 1). The number of cysts recovered from water having passed through the
|
|
filter devices ranged from zero to greater than 10^4 in individual tests. The
|
|
performance of individual devices was consistent as indicated by the standard
|
|
deviations for each of the three replicate test sets (Figure 1). The percentage
|
|
of cysts removed by the devices, corresponding to 100 minus the percent of cysts
|
|
recovered from the filtrate, was 100 percent for the First Need and Katadyn
|
|
filters and approximately 90 percent for the H2OK filter. The concentration of
|
|
cysts in the Pocket Purifier effluent was not statistically different from the
|
|
seed concentration.
|
|
|
|
The First Need and Katadyn filters were then subjected to a period of moderate
|
|
use and then retested. The volume of water processed during the simulated use
|
|
period was not the same for the two filters owing to differences in their
|
|
operation. The difference in volume had no apparent effect on performance of
|
|
the two filters. A total of 88 liters of tap water (turbidity of 0.3 NTU) was
|
|
filtered with the First Need. During the process it was back-flushed, as
|
|
recommended in package instructions, because the filtration rate decreased after
|
|
50, 71, and 75 liters had been filtered. After 88 liters had been processed,
|
|
the filtration rate was about 25 percent lower than when the filter was new, and
|
|
it was retested in that condition. The Katadyn filter was subjected to use by
|
|
filtering one liter of tap water four times a day for five days. At the end of
|
|
each day, the filter was cleaned according to package instructions by
|
|
disassembling, brushing the filter element, and allowing it to air-dry overnight
|
|
before reassembly. After the respective periods of use, these two filters were
|
|
tested in triplicate for efficiency of cyst removal. Performance of these
|
|
filters was the same, 100 percent cyst removal, when they were retested.
|
|
|
|
Cyst Inactivation
|
|
|
|
Contact Disinfection Devices - The effect of each of the contact disinfection
|
|
devices on G. lamblia cyst viability was limited. The Water Purifier
|
|
inactivated about 15 percent of the cysts added in 100 ml of upstream (low
|
|
turbidity) water; the H2OK filter inactivated about 5 percent of the cyst
|
|
challenge, and the Pocket Purifier inactivated about 2 percent of the cyst
|
|
challenge.
|
|
|
|
Chemical Disinfectants - The effectiveness of seven disinfecting chemical
|
|
preparations ranged from only a few percent to greater than 99.9 percent,
|
|
depending on the chemical and its concentration, the contact time, and the
|
|
disinfectant demand of the water (Figure 2). None of the disinfectants was more
|
|
than 90 percent effective after a contact time of 30 minutes. After eight-hour
|
|
contact, the four iodine-based disinfectants, each caused a greater than 99.9
|
|
percent reduction in viable cysts. The chlorine-based disinfectants were
|
|
clearly less effective than the iodine-based ones at both contact times.
|
|
|
|
Heating in Water - Experiments conducted with cysts of G. lamblia and of G.
|
|
muris indicated that the two species have virtually the same sensitivity to
|
|
inactivation by heating. Cysts at both species were completely inactivated by
|
|
heating to 70C for 10 minutes. Heating to 50C and 60C for 10 minutes produced
|
|
95 and 98 percent inactivation, respectively (Figure 3).
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Discussion
|
|
|
|
To remove Giardia cysts from water, one must use a filter with sufficiently
|
|
small pores to trap the cysts and sufficiently large capacity to produce a
|
|
useful volume of treated water before backwashing or replacement is necessary.
|
|
Although a number of manufacturers advertise that their filters remove Giardia
|
|
cysts, the only previously published account of filter performance was for the
|
|
Katadyn unit (6). Our filter evaluation study showed that only the First Need
|
|
and the Katadyn filters removed cysts with at least 99.9 percent effectiveness.
|
|
Under the same test conditions, the H2OK filter was approximately 90 percent
|
|
effective and the Pocket Purifier was less than 50 percent effective for cyst
|
|
removal. The analysis of viability for the cysts collected in the effluent of
|
|
the Water Purifier, H2OK, and Pocket Purifier indicates that passage through the
|
|
device did not significantly reduce the percentage of viable cysts.
|
|
|
|
The current study showed that none of the chemical treatments could inactivate
|
|
more than 90 percent of cysts with 30 minutes of contact time at 10C. At both
|
|
30 minutes and eight hours of contact time, the iodine-based disinfectants
|
|
inactivated a higher fraction of cysts than did the chlorine-based products.
|
|
All methods inactivated a lower percentage of cysts in cloudy or turbid water
|
|
than in clear water. All disinfectants performed better with eight hours of
|
|
contact time than with 30 minutes. Only the iodine-based compounds inactivated
|
|
99 to 99.9 percent of cysts, within eight hours of contact time for both turbid
|
|
and clear water. As observed by Jarroll, et al (5), the 2 percent tincture of
|
|
iodine was less effective than the other iodine preparations with 30 minutes of
|
|
contact time, but it was as effective as the others at eight hours. Comparison
|
|
of our results with those of Jarroll, et al (5), is complicated by differences
|
|
between test conditions used. However, our results generally indicate more
|
|
stringent requirements for effective inactivation of Giardia cysts. Differences
|
|
between cyst populations used in the two studies could account for the observed
|
|
differences, even though both were G. lamblia. Cysts produced in our
|
|
trophozoite - gerbil system had consistently high intrinsic viability (>80
|
|
percent), excysted efficiently when fresh (80 to 90 percent), and have appeared
|
|
more resistant to halogen disinfectants than reported previously (Ongerth J.E.:
|
|
unpublished).
|
|
|
|
The results of heat inactivation in our study correspond to previous reports
|
|
indicating that heating to between 60C and 70C kills Giardia cysts efficiently.
|
|
In addition, our data illustrate the correspondence between the fluorogenic
|
|
staining and in vitro excystation procedures for assessing cyst viability. When
|
|
applied to cysts of the same condition. Staining indicates a slightly higher
|
|
proportion of viable cysts than does excystation. Overall, however, the two
|
|
procedures provide comparable information.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Figure 1 - Effectiveness of Four Portable Water Filters for Removal of Giardia
|
|
Cysts from One-Liter Volumes of Water Each containing approximately 3x10^4 Cysts
|
|
(dotted line). [A bar chart showing the positive and negative controls and
|
|
results from the filters, on a log scale. The First Need and Katadyn results
|
|
and the negative control were all zero. The Pocket Purifier and the positive
|
|
control were approximately the same - i.e. the Pocket Purifier did not remove
|
|
cysts at all. The H2OK results were somewhat below the positive control,
|
|
actually -- due to the log scale -- indicating 90% removal.]
|
|
|
|
Figure 2 - Effect of Time and Disinfectant Concentration of Seven Chemical
|
|
Disinfectants on Survival of G. lamblia Cysts in Turbid and in Clear Water. [A
|
|
rather striking bar chart comparing chemical treatments under varying
|
|
conditions. The chlorine compounds were basically ineffective, with no
|
|
significant effect at 30 minutes; at 8 hours the Sierra was still totally
|
|
ineffective, the bleach killed about half the cysts, and the Halazone killed 70-
|
|
90% of the cysts (better in clear water). The iodine compounds were poor at 30
|
|
minutes in turbid water (half killed), only a little better at 30 minutes in
|
|
clear water (70-90% killed, with Potable Aqua the best), but completely
|
|
effective (100% killed) after 8 hours.]
|
|
|
|
Figure 3 - Inactivation of Giardia Cysts as a Function of Temperature (10-minute
|
|
exposures) as Indicated by Ethidium Bromide Staining and by in vitro
|
|
Excystation. [A line chart showing cyst survival at different temperatures.
|
|
Four combinations of Giardia species, source, and laboratory technique are
|
|
shown, but all show approximately the same results. 40C kills no cysts; 50C
|
|
kills a lot of cysts, 60C kills most cysts, 70C kills all cysts.]
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Acknowledgements
|
|
|
|
References to commercial products shall not be construed to represent or imply
|
|
the approval or endorsement by project investigators or sponsors.
|
|
|
|
Grant support was provided in part by the REI Environment Committee which
|
|
assumes no responsibility for the content of research reported in this
|
|
manuscript.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
References
|
|
|
|
(1) Craun GF: Waterborne outbreaks of giardiasis: current status. In: Erlandsen
|
|
SL, Meyer EA (eds): Giardia and Giardiasis. New York: Plenum Press, 1984; 243-
|
|
262.
|
|
|
|
(2) Kahn FH, Visscher BR: Water disinfection in the wilderness. West J Med
|
|
1975; 122:450-453.
|
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|
|
(3) Barbour AG, Nichols CR, Fukushima T: An outbreak of giardiasis in a group of
|
|
campers. Am J Trop Med Hyg 1980; 25:384-389.
|
|
|
|
(4) Ongerth JE, Butler R, Donner RG, Myrick R, Merry K: Giardia cyst
|
|
concentrations in river water. In: Advances in Water Treatment and Analysis,
|
|
Vol 15. Denver: Am Water Works Assoc, 1988; 243-261.
|
|
|
|
(5) Jarroll EL, Bingham AK, Meyer EA: Giardia cyst destruction: effectiveness of
|
|
six small quantity water disinfection methods. Am J Trop Med Hyg 1980; 29:8-11.
|
|
|
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(6) Schmidt SD, Meier PG: Evaluation of Giardia cyst removal via portable water
|
|
filtration devices. J Freshwater Ecol 1984; 2:435-439.
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|
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(7) Schaefer FW III, Rice EW, Hoff JC: Factors promoting in vitro excystation of
|
|
Giardia muris cysts. Trans R Soc Trop Med Hyg 1984; 78:795-800.
|
|
|
|
(8) Schupp DG, Erlandsen SL: A new method to determine Giardia cyst viability:
|
|
correlation of fluorescein diacetate and propidium iodide staining with animal
|
|
infectivity. Appl Environ Microbiol 1987; 53:704-707.
|
|
|
|
(9) Ongerth JE, Stibbs HH: Identification of Cryptosporidium oocysts in river
|
|
water. Appl Environ Microbiol 1987; 53:672-676,
|
|
|
|
(10) American Public Health Assoc: Chapter 408E In: Standard Methods for the
|
|
Examination of Water and Wastewater, 15th ed. Washington, DC: Am Public Health
|
|
Assoc, 1980; 309-310.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Appendix A: Water Filter characteristics Listed by Manufacturers on Packaging or
|
|
Instruction Insert
|
|
|
|
[Manufacturer column omitted. See text for this information.]
|
|
|
|
Name Filter Type Operating Operating Useful Restrictions
|
|
Mode Rate Life /Limitations
|
|
|
|
First Need 0.4 um microscreen hand pump 1 pt/min up to 800 A
|
|
plus adsorber pints
|
|
|
|
H2OK 6 um mesh, 3 in. gravity 1 qt/min 2000 gal A, B
|
|
activated carbon w/Ag
|
|
|
|
Katadyn 0.2 um ceramic, hand pump 1 qt/min many years A
|
|
Pocket Ag-impregnated
|
|
Filter
|
|
|
|
Pocket 10 um (nominal), halo- mouth - - A
|
|
Purifier genated resin (38% I), suction
|
|
Ag-impregnated carbon
|
|
|
|
Water Pur- Polystyrene resin bed gravity - 100 gal A, C
|
|
ifier (a) (46% I2 as I5)
|
|
|
|
A - Does not desalinate; not for saltwater or brackish water.
|
|
B - Pretreat with I2 for bacterially contaminated water.
|
|
C - Not for use with muddy water.
|
|
(a) Not described as a filter by package information.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Appendix B: Characteristics of Disinfectant Preparations
|
|
|
|
[Manufacturer column omitted. See text for this information.]
|
|
|
|
Name Active Chemical Recommended Application Total Halogen pH
|
|
Concentration (b)
|
|
(a), (mg/liter)
|
|
|
|
Polar Pure Crystalline iodine, 1-7 capfuls per quart 2.4 (1 6.1
|
|
99.5% depending on temperature cap/quart)
|
|
|
|
CEGDWT Tetraglycine hydro- 1 tablet per liter or 4.5 (1 5.6
|
|
periodate 16.7% (6.68% quart tab/quart)
|
|
titrable iodine)
|
|
|
|
Potable Tetraglycine hydro- 1 tablet per liter or 5.3 (1 5.6
|
|
Aqua periodate 16.7% (6.68% quart tab/quart)
|
|
titrable iodine)
|
|
|
|
2% Iodine Iodine 0.4 ml per liter 4.5 6.5
|
|
|
|
Sierra Calcium hypochlorite & 100 crystals (50 mg) 11.6 6.7
|
|
hydrogen peroxide Ca(OCl)2 + 6 drops H2O2
|
|
per gallon
|
|
|
|
Halazone p-dichloro-sulfamoyl 5 tablets per quart 7.5 6.7
|
|
benzoic acid, 2.87%
|
|
|
|
Chlorine sodium hypo-chlorite, 5 ml per gallon 3.9 7.1
|
|
bleach 5.25%
|
|
|
|
(a) As prepared according to package instructions.
|
|
(b) In water treated according to package instructions.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
Appendix C: Characteristics of Disinfectant Test Water
|
|
|
|
Source pH Turbidity (NTU) Chlorine Demand (a)
|
|
(mg.liter)
|
|
|
|
Spring-fed 6.8 0.09 0.3
|
|
|
|
Lake Washington 7.1 0.75 - 0.80 0.7
|
|
|
|
(a) 30 minutes, free chlorine demand (5).
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
The authors
|
|
|
|
Address reprint requests to Jerry E. Ongerth, PhD, PE, Assistant professor,
|
|
Department of Environmental Health, SB-75, University of Washington, School of
|
|
Public Health and Community Medicine, Seattle, WA 98195. Dr. Stibbs is with the
|
|
Department of Pathobiology, also at the School, and Mr. Macdonald is with the
|
|
Department of Medical Education, School of Medicine, both at the University of
|
|
Washington; Mr. Johnson is with the Department of Biological Chemistry, Johns
|
|
Hopkins School of Medicine, Baltimore; Dr. Frost is with the Office of
|
|
Environmental Programs, Department of Social and Health Sciences, Olympia, WA.
|
|
This paper, submitted to the Journal January 12, 1289, was revised and accepted
|
|
for publication June 22, 1989.
|
|
|
|
=====
|
|
|
|
REI Water Filter Chart
|
|
|
|
REI Water Filters Comparison Chart:
|
|
Katadyne MSR PUR First Need
|
|
------------+--------------+-------------+-------------+------------+
|
|
Minimum | .2 absolute | .1 absolute | 1.0 nominal |.4 absolute |
|
|
Pore Size | | | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Weight | 23 oz. | 19 oz. | 21 oz. | 14 oz. |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Number of | | | | |
|
|
Filter | 2 | 4 | 2 | 1 |
|
|
Elements | | | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Types of | Screen, |Foam, Screen | Glass Fibre,| Charcoal |
|
|
Elements | Ceramic |Carbon,Paper | Iodine resin| |
|
|
| |Membrane | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Cost Per | $.25 | $.28 | $.24 | $.37 |
|
|
Gallon | | | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Appr.Filter | | | | |
|
|
Life | 1000 | 500 | 500 | 100 |
|
|
(in Gallons)| | | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Approximate | | | | |
|
|
Filtering | 120 seconds | 90 seconds | 60 seconds | 90 seconds |
|
|
Time | | | | |
|
|
(in Quarts) | | | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Cost of | | Two Parts | | |
|
|
Replacement | $89.00 | $20.00 & | $40.00 | $24.00 |
|
|
Filter | | $30.00 | | |
|
|
------------+--------------+-------------+-------------+------------+
|
|
Price | $225.00 | $140.00 | $130.00 | $37.00 |
|
|
------------+--------------+-------------+-------------+------------+
|
|
|
|
For room reasons I left off two filters. Its specs are in order:
|
|
Basic Designs
|
|
1.0 absolute, 12 oz., 2, Granular active carbin & ceramic, $.07,
|
|
1000, 60 MINUTES!, $40.00, $60.00.
|
|
Timber Line:
|
|
2.0 absolute, 6 oz., 1, Spun Polypro, $.30,
|
|
100, 70 Seconds, $??.??, $30.00.
|
|
|
|
The filtering times are probably based on a new unit. Some units are
|
|
easy to clean, one can't be properly, and one can be cleaned on the fly.
|
|
|
|
Lower prices can be found elsewhere than REI. REI charges list mostly.
|
|
|
|
Also note some units are easier to use (and clean) than others.
|
|
|
|
Katadyn MSR PUR 1stNeed line Designs
|
|
min pore size .2 .1 1 + I .4 2 1
|
|
dry weight 23 oz 19 oz 21 oz 14 oz 6 oz 12 oz
|
|
seconds/qt 120 90 60 90 70 grav- (when new)
|
|
seconds/qt 120 180 60 180 140 ity (after usage)
|
|
filter life 1000 500 500 100 100 1000 (in gallons)
|
|
cost/gallon $.25 $.28 $.24 $.37 $.30 $.07
|
|
retail price $225 $140 $130 $ 38 $ 30 $ 65
|
|
replacement $ 89 $ 50 $ 40 $ 24 n/a $ 40 (filter cost)
|
|
# elements 2 4 3 1 1 2
|
|
elements screen foam screen carbon polypro carbon
|
|
ceramic screen glassfiber ceramic
|
|
carbon iodine
|
|
paper
|
|
|
|
Notes: 1st Need, Timberline, and Basic Designs require iodine to treat
|
|
bacteria and viruses. Katadyn and MSR require iodine to treat viruses.
|
|
Only PUR requires no additional iodine. With carbon elements, only MSR,
|
|
1st Need, and Basic Designs remove harmful chemicals.
|
|
|
|
TABLE OF CONTENTS of this chain:
|
|
|
|
9/ Water Filter wisdom <* THIS PANEL *>
|
|
10/ Words from Rachel Carson
|
|
11/ Snake bite
|
|
12/ Netiquette
|
|
13/ Questions on conditions and travel
|
|
14/ Dedication to Aldo Leopold
|
|
15/ Leopold's lot.
|
|
16/ Morbid backcountry/memorial
|
|
17/ Information about bears
|
|
18/ Poison ivy, frequently ask, under question
|
|
19/ Lyme disease, frequently ask, under question
|
|
20/ "Telling questions" backcountry Turing test
|
|
21/ AMS
|
|
22/ Words from Foreman and Hayduke
|
|
23/ A bit of song (like camp songs)
|
|
24/ What is natural?
|
|
25/ A romantic notion of high-tech employment
|
|
26/ Other news groups of related interest, networking
|
|
27/ Films/cinema references
|
|
28/ References (written)
|
|
1/ DISCLAIMER
|
|
2/ Ethics
|
|
3/ Learning I
|
|
4/ learning II (lists, "Ten Essentials," Chouinard comments)
|
|
5/ Summary of past topics
|
|
6/ Non-wisdom: fire-arms topic circular discussion
|
|
7/ Phone / address lists
|
|
8/ Fletcher's Law of Inverse Appreciation and advice
|
|
|
|
END.
|