Health authorities in Bangladesh urge villagers to boil surface water before drinking it, but a severe shortage of wood makes this process impossible for most people. Millions of people therefore must still use surface water and are at risk of cholera. However, scientist Rita Colwell came up with a method to filter out disease-causing organisms with an item available even in the poorest homes.
Dr. Rita Colwell
HYPOTHESIS: Simple Filtration Methods Will Reduce the Incidence of Cholera
Cholera is a severe disease that causes thousands of deaths each year. Symptoms of cholera include abdominal cramps, nausea, vomiting, dehydration, and shock. If untreated, death may occur after severe fluid and electrolyte loss. The responsible agent is a comma-shaped bacterium called Vibrio cholerae. In certain developing regions around the world where people must obtain untreated drinking water from streams and lakes, V. cholerae infection can occur.
Dr. Colwell, one of the world's leading cholera researchers, observed that V cholerae lives in association with microscopic copepods, which are a type of zooplankton. Dr. Colwell also showed that cholera outbreaks occurred seasonally in association with temperature changes and blooms of the copepod organisms.
Dr. Colwell and her colleagues knew that villagers often strained flavored beverages through a piece of fine cloth cut from an old, discarded sari, a woman's long flowing garment. Colwell came up with a hypothesis: Straining drinking water through an old piece of sari cloth could remove copepods and the associated cholera bacteria and prevent cases of cholera.
METHODS: Compare Filtration Methods
Colwell's team chose 142 villages in Bangladesh where people use untreated river or pond water for drinking and have high rates of cholera. They assigned over 45,000 participants to three groups. The
control group would continue to use unfiltered, untreated water. One experimental group would collect water in jars by tying four layers of sari cloth over the opening. The other experimental group would collect water in containers covered by filter fabric designed to remove copepod-sized organisms. Field workers collected medical data on cholera cases during the study period.
RESULTS: Cholera Cases Are Reduced
The team compared the incidence of cholera for the control group with that of the two experimental groups. They found that the control group had the usual number of cholera cases (about 3 per 1,000 people per year). However, using either nylon filtration cloth or sari cloth cut the number of cases in half. Interestingly, old cloth worked better than new cloth because older fibers soften, the pore size is reduced, and more copepods and attached bacteria are trapped in the pores.
CONCLUSION: Saris Can Reduce the Incidence of Cholera
Rita Colwell and her team concluded that saris are a simple, practical solution to a serious global problem. They are currently looking at ways to expand this filtration idea to other parts of the world. Women don't wear saris everywhere, but old cloth is available in virtually every home.
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