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Re: [at-l] To filter or not?

In a message dated 98-03-09 14:47:10 EST, Milt Webb wrote:

>  Roland sent questionaires to 136 thru-hikers and one of the most
>  interesting (and I'm sure controversial) findings had to do with water
>  purification, methods used and incindent of GI illness on the trail.
>  
>  Briefly, 30% of those FILTERING their water reported GI illness compared
>  to only 27% for those using NO TREATMENT at all.
>  
>  Did that get anyone's attention???
>  The highest occurrence of GI problems were reported by those using only
>  chlorine to treat the water.
___________________________________________________________________

The First Need Filter (used by most) had a lot of problum in 1989. New filters
were cloging after filtering just a few gallons. Filters were leaking, I
observed a couple of times, were both filtered and unfiltered water was going
into a hikers water bottle. 

The infomation from these questionnaire's is questionable. 

GI illness can be from other causes, not related to water

In 1989 there were signs posted on the Antietam Creek (Antietam Shelter)
stating that GIARDIA had been found in the water. All but one thru-hiker
filtered their water. This hiker came down with Giardiasis,about a week later.

I filtered most of my water, what water I didn't filter was boiled. I have
used the same  Katadyn PF water filter on three thru-hikes. I have not came
down with any GI type illness.
____________________________________________________________________
How do people get giardia? (From the Vermont Department of Health)

People and animals infected with giardia pass it in their stool. 

People become infected:

•directly by hand-to-mouth transfer from the stool of an infected person. That
is, hands can be soiled when using the toilet. If hands are not thoroughly
washed, the giardia can be transferred to food, drink or items handled or
eaten by another person. 

•indirectly by swallowing water that has been contaminated with stool that
contains giardia (when swimming in ponds, drinking from streams, etc.). 

•What are common sources of giardia? •drinking contaminated water from
streams, rivers, springs and ponds 

•infected household and day care contacts, especially children in diapers (See
Giardiasis in Day Care Centers, also available from the Health Department.) 

•swimming in untreated surface water, such as wading pools, ponds, rivers,
streams or lakes 

•private water systems (wells or springs) that are not correctly installed or
maintained 

The cyst is a tough, protective package that allows the protozoa to survive
until it finds another animal gut to infect. Giardia cysts can survive for
weeks in cold water, and they're resistant but not immune to treatment by
chlorine, iodine and other chemicals. Fortunately for humans, they can be
killed by boiling the water and they can be filtered out.

____________________________________________________________________
Giardiasis

Giardiasis is the disease caused by Giardia lamblia, a single-celled animal
that moves with the aid of five flagella. Human giardiasis may involve
diarrhea within a week of ingestion of the cyst, which is the environmental
survival form and infective stage of the organism. In contrast to most
bacterial illnesses where hundreds to thousands of organisms must be consumed
to produce illness, ingestion of one or more cysts may cause the disease. Cool
moist conditions favor the survival of 
the organism. Giardiasis is more prevalent in children than in adults,
possibly because many individuals seem to have a lasting immunity after
infection. This organism is implicated in 25 percent of all cases of
gastrointestinal disease and may be present in other cases asymptomatically. 

Wildbill
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