From: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
Subject: [l/m 9/9/91] Distilled Wisdom (9/28): Water filters & Giardia	XYZ
Followup-To: poster
Organization: NAS Program, NASA Ames Research Center, Moffett Field, CA
Date: Thu, 9 Apr 92 11:20:50 GMT
Reply-To: tut@sun.com (Bill Tuthill)

Copyright (c) 1991 by Bill Tuthill

Unpurified drinking water may contain four things that pose health risks:
protozoan parasites (e.g. giardia), toxic bacteria, harmful viruses, and
poisonous chemicals.  Of the methods available in the field, only boiling
and iodine are entirely effective against the first three, and only charcoal
filtration is effective against the fourth.

The First Need(R) water filter is cheap (less than $40), but is effective
merely against protozoan parasites.  Its .4 micron filter pores are smaller
than giardia cysts at 3.5 microns, but larger than some bacteria, such as
E. coli at .3 to .9 microns.  The First Need's charcoal canister is not big
enough to be effective against poisonous chemicals -- you need a pound of
charcoal for this -- so it just adds unnecessary weight, and provides a
potential haven for the growth of harmful bacteria.  If you own a First Need
filter, flush it with iodine after each trip.

The Katadyn(R) water filter is expensive (over $200), but is completely
effective against bacteria as well as giardia.  Moreover, it can be cleaned
after it clogs up.  The Katadyn is effective at removing smaller bacteria
such as E. coli.  However, its .2 micron filter is not effective against
any virus.  If you travel abroad (to Nepal for example), you risk viral
infections such as Hepatitis A and Hepatitis non-A non-B, among others.

MSR has a new water filter, which may be superior to the Katadyn.  Results
from the field aren't in yet.

To be entirely safe, water should be boiled for at least five minutes.
Giardia is killed in less than a minute at 176 degrees, well under the
boiling point.  Bacteria and viruses last somewhat longer, but are probably
killed in less than five minutes at 190 degrees.  Some viruses may last
longer; nobody knows.  At 10,000 feet water boils at 194 degrees; above
this altitude boil water about an extra minute for each 1000 feet.

+If you have neither the time nor the inclination to boil water, iodine
+is equally effective.  After 15 minutes (30 minutes for very cold water),
+a sufficient dose of iodine kills all protozoa, bacteria, and viruses.
+One readily-available choice is Potable-Aqua(R) tablets.  Dissolve one
+tablet per liter of water (two tablets if cloudy) and wait.  The problem
+with iodine tablets is that they degrade upon contact with moisture, so
+keep that bottle dry, and discard it upon returning home.

Avoid halazone and Clorox, because chlorine is volatile, slow to disinfect,
and works differently against protozoa and viruses at various pH levels.
It also reacts with organic compounds to form carcinogenic chloramines.
Also avoid tincture of iodine, which contains more sodium iodide than pure
iodine; sodium iodide has no disinfectant properties.

Iodine is not highly toxic, and in fact is an essential ingredient of
human nutrition.  However, continuous ingestion of large doses may cause
health problems, so don't iodinate all your water for more than a few
months at a time.

The accepted concentration for iodine disinfection is 8 milligrams per
liter, but this is mostly to get rid of protozoan parasites.  A good way
to reduce overall iodine consumption and minimize that iodine flavor is
to filter first, then use a low concentration of iodine to get rid of
bacteria and viruses.  For this, a concentration of .5 mg/L is deemed
adequate, so one capful of PolarPure or one Potable-Aqua tablet should
disinfect around 16 liters of lightly filtered water.  The Timberline(R)
filter, with its 2 micron pores, is fine for removing protozoa.

Giardia has become a well-known, almost fashionable, outdoor hazard.
Many people who experience gastro-intestinal problems after drinking
bad water think they have contracted giardia.  In many cases they have
contracted something else.  Since the only FDA-approved treatment for
giardia (Flagyl) is very nasty, it's wise to make sure you really have
giardia before taking Flagyl.  Most low-grade bacterial infections go away
on their own, and Flagyl is ineffective against viral infections.  One
alternative to Flagyl is quinacrine.  In many parts of the world (Asia
for example) Tinidazole is available, and is preferable to Flagyl because
it is less toxic and quicker acting.

[This information based on "Medicine for Mountaineering", various owner's
pamphlets, and personal experience.]

TABLE OF CONTENTS of this chain:

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/ Learning (3)
8/ Fletcher's Law of Inverse Appreciation and advice
9/ Water Filter wisdom					<* THIS PANEL *>
10/ Words from Rachel Carson
11/ Scouting		<pending>
12/ Netiquette
13/ Questions on conditions and travel
14/ Dedication to Aldo Leopold
15/ Leopold's lot.
16/
17/ Information about bears
18/ Poison ivy, frequently ask, under question
19/ Lyme disease, frequently ask, under question
20/ "Telling questions" backcountry Turing test (under construction)
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)

GIARDIASIS

GIARDIASIS: By Dennis D. Juranek, Chief, Epidemiology Activity
Parasitic Diseases Branch
Division of Parasitic Diseases
Centers for Disease Control

Transmission and Control

Introduction

During the past fifteen years giardiasis has been recognized as one of the
most frequently occurring waterborne diseases in the United States (1).
Giardia lamblia have been discovered in the United States in places as far
apart as Estes Park, Colorado (near the Continental Divide); Missoula,
Montana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; and Pittsfield
and Lawrence, Massachusetts just to name a few. In light of recent large
outbreaks of waterborne giardiasis, it seem timely to present reliable
information on the way in which giardiasis is acquired, treated, and
prevented.

Giardiasis: Prevalence and Symptoms

Giardiasis is a disease caused by a one-celled parasite with the scientific
name Giardia lamblia. The disease is characterized by intestinal symptoms
that usually last one week or more and may be accompanied by one or more of
the following: diarrhea, abdominal cramps, bloating, flatulence, fatigue, and
weight loss (see Table 1). Although vomiting and fever are listed in Table 1
as relatively frequent symptoms, they have been uncommonly reported by people
involved in waterborne outbreaks of giardiasis in the United States. Table 1
also suggests that 13 percent of patients with giardiasis may have blood in
their stool. Giardia, however, rarely causes intestinal bleeding. Therefore,
blood in the stool of a patient with giardiasis almost always indicates the
presence of a second disease.

While most Giardia infections persist only for one or two months, some people
undergo a more chronic phase, which can follow the acute phase or may become
manifest without an antecedent acute illness. The chronic phase is
characterized by loose stools, and increased abdominal gassiness with
cramping, flatulence and burping. Fever is not common, but malaise, fatigue,
and depression may ensue (2). For a small number of people, the persistence of
infection is associated with the development of marked malabsorption and
weight loss (3). Similarly, lactose (milk) intolerance can be a problem for
some people. This can develop coincidentally with the infection or be
aggravated by it, causing an increase in intestinal symptoms after ingestion
of milk products.

Some people may have several of these symptoms without evidence of diarrhea or
have only sporadic episodes of diarrhea every 3 or 4 days. Still others may
not have any symptoms at all. Therefore, the problem may not be whether you
are infected with the parasite or not, but how harmoniously you both can live
together, or how to get rid of the parasite (either spontaneously or by
treatment) when the harmony does not exist or is lost.

Medical Treatment

Three drugs are available in the United States to treat giardiasis: quinacrine
(Atabrine*), metronidazole (Flagyl*), and furazolidone (Furoxone*). All are
prescription drugs. In a recent review of drug trials in which the efficacies
of these drugs were compared, quinacrine produced a cure in 93% of 129
patients, metronidazole cured 92% of 219, and furazolidone cured 84% of 150
patients (4). Quinacrine is generally the least expensive of the anti-Giardia
medications but it often causes vomiting in children younger than 5 years
old. Although the treatment of giardiasis is not an FDA-approved indication
for metronidazole, the drug is commonly used for this purpose. Furazolidone
is the least effective of the three drugs, but is the only anti-Giardia
medication that comes as a liquid preparation, which makes it easier to
deliver the exact dose to small children and makes it the most convenient
dosage form for children who have difficulty taking pills. Cases of chronic
giardiasis refractory to repeated courses of therapy have been noted, one of
which responded to combined quinacrine and metronidazole treatment (5).

(*) Use of trade names is for purposes of identification only.

Etiology and Epidemiology

Giardiasis occurs worldwide. In the United States, Giardia is the parasite
most commonly identified in stool specimens submitted to state laboratories
for parasitologic examination. From 1977 through 1979, approximately 4% of 1
million stool specimens submitted to state laboratories were positive for
Giardia (6). Other surveys have demonstrated Giardia prevalence rates ranging
from 1 to 20% depending on the location and ages of persons studied.
Giardiasis ranks among the top 20 infectious diseases that cause the greatest
morbidity in Africa, Asia, and Latin America (7); it has been estimated that
about 2 million infections occur per year in these regions (8).

People who are at highest risk for acquiring a Giardia infection in the United
States may be placed into five major categories:

1) People in cities whose drinking water originates from streams or
   rivers and whose water treatment process does not include
   filtration, or filtration is ineffective because of malfunctioning
   equipment. 
2) Hikers/campers/outdoorspeople.
3) International travelers
4) Children who attend day-care centers, day-care center staff, and
   parents and siblings of children infected in day-care centers. 
5) Homosexual men.

People in categories 1, 2, and 3 have in common the same general source of
infections, i.e., they acquire Giardia from fecally contaminated drinking
water. The city resident usually becomes infected because the municipal water
treatment process does not include a filter that is necessary to physically
remove the parasite from the water. The number of people in the United States
at risk (i.e., the number who receive municipal drinking water from unfiltered
surface water) is estimated to be 20 million. International travelers may
also acquire the parasite from improperly treated municipal waters in cities
or villages in other parts of the world, particularly in developing
countries. In Eurasia, only travelers to Leningrad appear to be at increased
risk. In prospective studies, 88% of U.S. and 35% of Finnish travelers to
Leningrad who had negative stool tests for Giardia on departure to the Soviet
Union developed symptoms of giardiasis and had positive tests for Giardia
after they returned home (10,11). With the exception of visitors to Leningrad,
however, Giardia has not been implicated as a major cause of traveler's
diarrhea. The parasite has been detected in fewer than 2% of travelers who
develop diarrhea. Hikers and campers risk infection every time they drink
untreated raw water from a stream or river.

Persons in categories 4 and 5 become exposed through more direct contact with
feces of an infected person, e.g., exposure to soiled diapers of an infected
child (day-care center-associated cases), or through direct or indirect
anal-oral sexual practices in the case of homosexual men.

Although community waterborne outbreaks of giardiasis have received the
greatest publicity in the United States during the past decade, about half of
the Giardia cases discussed with staff of the Centers for Disease Control in
the past 2 to 3 years have a day-care center exposure as the most likely
source of infection. Numerous outbreaks of Giardia in day-care centers have
been reported in recent years. Infection rates for children in day-care
center outbreaks range from 21 to 44% in the United states and from 8 to 27%
in Canada (12,13,14,15,16,17). The highest infection rates are usually
observed in children who wear diapers (l to 3 years of age). In one study of
18 randomly selected day care centers in Atlanta (CDC unpublished data), 10%
of diapered children were found infected. Transmission from this age group to
older children, day-care staff, and household contacts is also common. About
20% of parents caring for an infected child will come infected.

It is important that local health officials and managers of water utility
companies realize that sources of Giardia infection other than municipal
drinking water exist. Armed with this knowledge, they are less likely to make
a quick (and sometimes wrong) assumption that a cluster of recently diagnosed
cases in a city is related to municipal drinking water. Of course, drinking
water must not be ruled out as a source of infection when a larger than
expected number of cases are recognized in a community, but the possibility
that the cases are associated with a day-care center outbreak, drinking
untreated stream water, or international travel should also be
entertained.

Parasite Biology

To understand the finer aspects of Giardia transmission and the strategies for
control, one must become familiar with several aspects of the parasite's
biology. Two forms of the parasite exist: a trophozoite and a cyst, both of
which are much larger than bacteria (see Figure 1). Trophozoites live in the
upper small intestine where they attach to the intestinal wall by means of a
disc-shaped suction pad on their ventral surface. Trophozoites actively feed
and reproduce at this location. At some time during the trophozoite's life,
it releases its hold on the bowel wall and floats in the fecal stream through
the intestine. As it makes this journey, it undergoes a morphologic
transformation into an egglike structure called a cyst. The cyst, which is
about 6 to 9 micrometers in diameter x 8 to 12 micrometers (1/100 millimeter)
in length, has a thick exterior wall that protects the parasite against the
harsh elements that it will encounter outside the body. This cyst form of the
parasite is infectious for other people or animals. Most people become
infected either directly by hand-to-mouth transfer of cysts from the feces of
an infected individual, or indirectly by drinking feces-contaminated water.
Less common modes of transmission included ingestion of fecally contaminated
food and hand-to-mouth transfer of cysts after touching a fecally contaminated
surface. After the cyst is swallowed, the trophozoite is liberated through
the action of stomach acid and digestive enzymes and becomes established in
the small intestine.

Although infection after the ingestion of only one Giardia cyst is
theoretically possible, the minimum number of cysts shown to infect a human
under experimental conditions is ten (18). Trophozoites divide by binary
fission about every 12 hours. What this means in practical terms that if a
person swallowed only a single cyst, reproduction at this rate would result in
more than 1 million parasites 10 days later, and 1 billion parasites by day 15.

The exact mechanism by which Giardia causes illness is not yet well
understood, but is not necessarily related to the number of organisms
present. Nearly all of the symptoms, however, are related to dysfunction of
the gastrointestinal tract. The parasite rarely invades other parts of the
body, such as the gall bladder or pancreatic ducts. Intestinal infection does
not result in permanent damage.

Transmission

Data reported to the CDC indicate that Giardia is the most frequently
identified cause of diarrheal outbreaks associated with drinking water in the
United States. The remainder of this article will be devoted to waterborne
transmission of Giardia. Waterborne epidemics of giardiasis are a relatively
frequent occurrence. In 1983, for example, Giardia was identified as the
cause of diarrhea in 68% of waterborne outbreaks in which the causal agent was
identified (19). From 1965 to 1982, more than 50 waterborne outbreaks were
reported (20). In 1984, about 250,000 people in Pennsylvania were advised to
boil drinking water for 6 months because of Giardia-contaminated water.
Many of the municipal waterborne outbreaks of Giardia have been subjected to
intense study to determine their cause. Several general conclusions can be
made from data obtained in those studies. Waterborne transmission of Giardia
in the United States usually occurs in mountainous regions where community
drinking water is obtained from clear running streams, is chlorinated but is
not filtered before distribution. Although mountain streams appear to be
clean, fecal contamination upstream by human residents or visitors, as well as
by Giardia-infected animals such as beavers, has been well documented. It is
worth emphasizing that water obtained from deep wells is an unlikely source of
Giardia because of the natural filtration of water as it percolates through
the soil to reach underground cisterns. Well-water sources that pose the
greatest risk of fecal contamination are those that are poorly constructed or
improperly located. A few outbreaks have occurred in towns that included
filtration in the water treatment process, but the filtration was not
effective in removing Giardia cysts because of defects in filter construction,
poor maintenance of the filter media, or inadequate pretreatment of the water
before it was filtered. Occasional outbreaks have also occurred because of
accidental cross-connections between water and sewerage systems.

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. 

From: donehoo@olivee.ATC.Olivetti.Com (Doyle W. Donehoo)
Subject: REI Water Filter Chart

I only listed the Filters, and left off the chemical treatment stuff.

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.


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