Study Reveals: Simple Filter Can Halve Cholera Cases

Forcing water through a simple filter made from the cloth of old saris can reduce cholera cases by about half, according to a study of rural villages in Bangladesh where cholera is a major health problem.

Researchers suggest the sari filters also may reduce other gastrointestinal illness.

The study from the Proceedings of the National Academy of Sciences, compared the effect of filtering pond or river water through a modern nylon mesh and through old, much-washed sari cloth and found that the sari solution was best.

"Sari cloth is cheaper and we found that it is much more effective than the nylon mesh," said Rita R. Colwell, a professor of microbiologist at the University of Maryland, College Park, and primary author of the study. "The nylon costs only a few dollars a year, but a few dollars can be a week's wages in these Bangladesh villages."

Colwell said that researchers discovered in laboratory studies that most of the cholera bacteria in ponds, rivers and other standing water was attached to or in the gut of a copepod, a type of zooplankton commonly found in standing water.

When people drink unfiltered water, she said, they swallow the copepods and introduce cholera bacteria into their system. The germ can thrives, releasing a toxin that causes extreme diarrhea and cramping.

Filtering the copepod, said Colwell, reduced by the cholera rate by at least half. She said there also was some evidence that other types of germs were removed because women in the villages with sari-filtered water said there was less diarrhea and other digestive problems.

In modern hospitals, cholera is easily controlled, but the untreated disease kills 50 to 80 percent of those infected. It is most lethal for children under five and for the elderly.

Colwell said the rural Bangladesh villages where the filter system was tested are many hours of hard travel away from good medical care and finding a simple way to combat cholera could have a major impact on the lives of people there.

Dr. John Mekalanos, a cholera expert and professor at the Harvard Medical School, said Colwell and her co-authors "have made a major contribution to the control of cholera" by demonstrating an easy way for rural, Third World people to protect themselves from a major health problem.

"Anytime you can reduce a life-threatening disease by (50 percent) with something this simple it could make a big difference in the region and elsewhere in the world," Mekalanos said.

There were 184,000 cases of cholera reported from 58 countries in 2001, according to the World Health Organization. More than 2,700 people died. However, Bangladesh was not included in these statistics, said Colwell, and it is thought the cholera rate and the number of deaths from the disease are very high. Mekalanos estimated that there are a million cases of cholera in Bangladesh annually and thousands of unreported deaths.

In the study, Colwell and her colleagues selected 65 villages where cholera was a major threat. In 27 of the villages, women were instructed to use bits of sari cloth, folded eight times, as a filter when they captured household water from ponds, lakes or rivers. Twenty-five villages were instructed to use the nylon filters, and 13 villages received no filtering instructions and continued to gather water in the traditional way. There were about 44,000 people in each of the three arms of the study.

After 18 months, the rate of cholera in villages using the sari filters was about .65 cases per 1,000 people per year. The rate was about .79 cases in the villages using nylon filters, and about 1.16 cases per 1,000 people in the control villages.

Colwell said the researchers traced the origin of each of the cholera cases and found that the majority of those who got sick in the sari-filtered villages had visited villages where they drank unfiltered water.

She said the rate of cholera was extremely low among people who drank only the sari-filtered water.

"We found in the laboratory that we could remove more than 99 percent of the bacteria with the sari cloth," said Colwell.

A sari is the garment favored by most Hindu women. It consists of a long piece of cloth wrapped around the body, with one end forming a shirt and the other end draped across the front and over one shoulder. The cotton fabric is a lightweight gauzelike material.

Colwell said experiments showed that old sari cloth filtered better than new cloth. As the sari is washed repeatedly, she said, the spaces between threads in the cloth mesh narrow and trap finer particles. Folded eight times, she said, the sari cloth filters particles as small as 20 microns. A human hair is 25 to 50 microns in diameter.

"We tried other material, but the sari was by far the most effective," said Colwell. And it is available in most Bangladesh households. "Every woman there wears a sari."


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