Study reveals sari cloth filtration reduces cholera. (Environmental Intelligence).

Filtering water with a folded piece of old cloth before drinking it cuts the rate of cholera contraction by half, according to a three-year study in 65 Bangladeshi villages published in January 2003 in the U.S. journal Proceedings of the National Academy of Sciences.

The finding has the potential to save thousands of lives annually. Fabric from saris, the flowing, colorful garments South Asian women often wear, was cheap and readily available to the 133,000 people who participated in the study, and comparable fabrics could function as filters for populations at risk for cholera around the world.

Ingesting a high dose of the waterborne bacteria Vibrio cholerae O1 produces cholera, an infection that causes severe dehydration brought on by acute diarrhea and vomiting. Left untreated, cholera can kill a person in 24 hours. Nearly 124,000 cases of the disease were reported in 2002, including 3,763 deaths, according to the World Health Organization (WHO). A large majority of these appeared on the African continent and in India. These statistics are highly unreliable, however, because many countries, including Bangladesh, do not report cholera data to the WHO.

The sari cloth traps not V. cholerae themselves but copepods, a type of zooplankton onto whose mouths, surfaces, and egg cases the vibrio attach. Although much of the vibrio did remain free in the filtered water, their number often diminished enough to fall short of an infective dose, estimated at [10.sup.4] and [10.sup.6] V. cholerae. The dilution lowered the rate of cholera infection by 48 percent. For those who did contract cholera via filtered water, the severity of the disease appears to have lessened, the report says.

Electron microscopy had revealed that sari cloth, when folded four to eight times, would create a filter of approximately 20 mm pore size, removing all copepods--and the cholera-causing bacteria attached to them--from the water. The old saris used in the experiment were expected to be more effective than new ones, their laundered fabric resulting in a smaller pore size.

Rivers and ponds are a common source of drinking water for the villages in rural Matlab, Bangladesh. Boiling water, which kills all waterborne microorganisms, is often impossible for the villagers, who are hard-pressed to find dry wood for fuel or the money to buy it. High concentrations of arsenic in the groundwater make well sources a poor alternative. (See "Poisoned Waters," January/February 2003.)

The experiment, conducted by researchers from the University of Maryland in the United States and the International Centre for Diarrhoeal Disease in Bangladesh, compared the presence of cholera in households that filtered their water with old saris to households that used a nylon mesh filter and to those that had no filter at all. The nylon mesh filter was nearly as effective as the sari cloth in reducing cholera, but that material is more costly and harder to find in rural Bangladesh than material from saris.