U.S. Water News Online
NEW YORK -- People in developing nations can cut their risk
of cholera by filtering their drinking water through old clothing,
new study findings from Bangladesh suggest.
The scientists found that such makeshift filters could cut the
number of cholera infections by about half compared with no
Cholera is transmitted through food and water contaminated with
Vibrio cholerae bacteria. While the potentially life-threatening
diarrhea is rare in developed countries, it remains common in
less-developed parts of the world.
Cholera cases occurred in 58 countries in 2001, according to a
survey conducted by the World Health Organization, notes Dr. Rita R.
Colwell, of the University of Maryland Biotechnology Institute in
Baltimore, and colleagues.
According to a report in the online edition of the journal
Proceedings of the National Academy of Sciences, Colwell and
colleagues evaluated the effectiveness of using cloth filters to rid
contaminated water of cholera.
In the study, more than 2,000 households in rural villages in
Bangladesh were trained to fold sari cloth to form eight layers. A
sari is an outer garment worn mainly by women in India, Pakistan and
Bangladesh. A long cotton fabric, one end of the cloth wraps around
the waist to form a skirt and the other is draped over one shoulder
or is used to cover the woman's head.
The cloth filter was then placed over the neck of a water
collecting pot. When the vessel "is dipped in a pond, canal, or
river, the water enters the container only by passing through the
sari cloth," the authors write.
In the study, older fabric that had been washed repeatedly had
smaller pore sizes compared to newer fabric, and was less likely to
let bacteria into the water-collecting pots.
Over an 19-month period the researchers monitored the number of
cholera infections reported by the villagers. This group was compared
to a similar number of households that used nylon filters to remove
bacteria from drinking water or no filtration system.
"We estimated that the sari group had a cholera rate approximately
52% of the control (those without any filters), or cholera was
reduced by about half," the authors report.
In general, the reduction of cholera cases among those using sari
filtration was similar to those using nylon filters.
The reason for the success of the sari cloth filtration system
rests primarily on the fact that cholera bacteria most often attach
themselves to larger water organisms called plankton. Therefore,
filtering out the plankton also reduces the amount of cholera
bacteria in the water.
Moreover, infection with the bacteria is dose dependent. In other
words, the more organisms that are consumed, the more likely an
individual is to get sick. So even though the cloth filters don't
remove 100 percent of the bacteria, the reduction brought by the
makeshift filters is enough to reduce the likelihood of illness.
Such a filtration system is attractive largely because it is so
inexpensive and easy to construct. In addition, it provides another
option for treating water for villagers who are unwilling to
sacrifice hard-to-come-by wood for boiling water -- the more
effective way to rid water of harmful microorganisms, according to
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