The Waterworks Flu

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Only the microbiologists were happy last week as Milwaukee turned into a huge, spontaneous laboratory for learning more than anyone wanted to know about what a parasite can do to an unsuspecting population. Or if they were not exactly happy, then at least very busy, trying to explain how something so tiny could cause troubles so huge. DON'T DRINK THE WATER, shouted the city's headlines, as thousands of area residents, including the mayor's wife and infant son, contracted a flulike illness that has emptied drugstores of antidiarrhea medications and sent hundreds to hospital emergency rooms. One businessman actually brought water back from Chicago, some 90 miles away. Schools shut off drinking fountains; the Culligan man showed up outside a local TV station to distribute distilled water; and a line formed outside the old Pryor Avenue Iron well, one of the city's few sources of artesian water.

! The culprit, test results show, is a tiny parasite with a big name: cryptosporidium. The oocysts (parasite versions of eggs) of this pesky protozoan can be removed only through filtration. Unlike bacteria, they are not readily killed by chlorine. Furthermore, the tests that water-purification plants routinely rely on to detect biological contaminants do not pick up the presence of cryptosporidium. What makes the parasite especially nasty, explains microbiologist Dean Cliver of the University of Wisconsin, Madison, is that the oocysts do not hatch in water -- in this case Lake Michigan water -- but remain dormant until they are swallowed by some thirsty creature.

Next, digestive juices dissolve the thick wall of the oocysts, triggering a growth cycle that ends in a reproductive orgy. Tiny protozoans attach themselves to intestinal walls and begin to mature. While there, scientists speculate, they probably exude some irritating toxin -- just the thing to cause the host organism to expel the oocysts produced by the adult organisms through diarrhea and vomiting. "A sick person will produce 100 million oocysts a day," marvels Cliver.

Milwaukee's waterworks flu is not the first outbreak of cryptosporidiosis in this country, nor is it likely to be the last. Indeed, Walter Jakubowski, a parasitology expert for the Environmental Protection Agency, believes that most surface water is now contaminated with the parasite. "It's so widespread," he observes, "that you just can't keep it out." In 1984 the Atlanta-based Centers for Disease Control investigated several outbreaks in day-care centers in five states. In 1987 an outbreak in Carrollton, Georgia, made 13,000 people absolutely miserable. Two Oregon towns, Medford and Talent, experienced an outbreak last year. In all, 21 million Americans who drink unfiltered water from lakes and rivers may be at risk.

For healthy adults, the symptoms are usually mild enough to go unnoticed. But for others -- notably, infants, AIDS patients and the elderly -- cryptosporidiosis can be serious, sometimes life threatening. "The wasting syndrome we see in so many AIDS patients," observes Dr. John Flaherty, an infectious-disease expert at the University of Chicago, "is most commonly due to cryptosporidiosis."