Risks Misjudged in Cholera Epidemic

Health officials in Peru appear to have misjudged the relative risks of water chlorination on one hand and microbial contamination on the other, which may have helped begin a cholera epidemic that is now sweeping Peru and other countries in South and Central America.

The decision by Peruvian officials to halt chlorination of much of the country's drinking water is being blamed for the outbreak of cholera in January 1991. More than 300,000 cases of cholera have been reported and more than 3,500 lives claimed by the epidemic. Spread of the disease in South and Central America is expected to be a problem for years to come.

According to a report in Nature, Pan American Health Organization officials believe that the bacteria first arrived with a Chinese freighter that dumped its contaminated bilge water into the harbor of Lima, Peru. The organisms quickly spread to fish and shellfish and probably first contaminated humans in servings of raw fish called ceviche. Once humans were contaminated, the bacteria infected the water supply, which amplified its spread among the population.

Although Peru has good water-filtration technology and pumps safe water into the drinking water system, old pipes and unchlorinated open wells appear to have allowed the cholera bacteria to enter the water supply after filtration, Nature reported.

The U.S. Food and Drug Administration reports that cholera will not become an epidemic in the United States because clean drinking water flows into nearly every home, sanitation systems are available to the vast majority of the population and FDA laboratories test for the cholera bacteria in imported food. However, the FDA has expanded its import sampling for cholera for products from Latin American countries.

In the past, there have been no known problems with food commercially imported to the United States from infected countries because Latin American exporters often rinse produce in chlorinated water. Also, cholera bacteria die on fruits and vegetables in 10 days or less, so they cannot survive the two-week trip from South America to U.S. ports. The bacteria can live somewhat longer in seafood.

Sampling for cholera initially has focused on fruits, vegetables, water/ice, and seafood products from Mexico and directed in only two districts-Dallas and Los Angeles. As an added precaution, FDA will conduct cholera sampling of Central American products directed toward three additional districts: New York, Orlando and New Orleans.

Chlorine's Risks and Benefits

Chlorine is a disinfectant that is capable of killing the bacterium that causes cholera, a marine organism called Vibrio cholerae 01. However, chlorine also can react with the byproducts of organic decay present in most water supplies to produce several suspected animal carcinogens, including chloroform. The U.S. Environmental Protection Agency regulates levels of one class of these chlorine-based compounds, called trihalomethanes (THMs). Major water systems in the United States must not exceed 100 parts per billion (ppb) of THMs. EPA is currently reevaluating theoretical cancer risks associated with water disinfection. Yet, according to Nature, most epidemiologists agree that a relatively small risk of cancer is preferable to the possibility of a microbial epidemic.

Peru's Risk Analysis

Based on EPA's studies showing a theoretical cancer risk associated with THMs, Peruvian officials halted chlorination of many of Lima's wells. This apparent misjudgment of relative risks has focused attention on the balancing of microbial and carcinogenic risks in water treatment.

"Chlorination and disinfection of the water supplies are one of the major public health success stories of the century," said Carol Henry, Ph.D., director of the International Life Sciences Institute's (ILSI) Risk Science Institute, at a National Academy of Sciences meeting. "To start altering this in some way has very grave and immediate consequences." In August 1992, ILSI is convening an international conference on balancing chemical and microbial risks in water supplies.

The experience in Peru lends perspective to innumerable risk management situations. As Nature observed, "This sobering case of risk assessment gone wrong is forcing U.S. and international health officials to come to grips with the flaws in what most agree is a haphazard process of balancing real and theoretical public health risks."