It went to a business meeting in Houston. It stopped by a bridal shower on Cape Cod. It put in an appearance at a New York City restaurant, attended a luncheon in Charleston, South Carolina, and crashed a catered party in central New Jersey. At dozens of social gatherings last summer, the intestinal parasite Cyclospora cayetanensis was an unwelcome guest, causing more than 900 cases of food poisoning in 20 states and two Canadian provinces between May and July. No one died from the poisoning, which can be treated with antibiotics, but one woman described its accompanying cramps as worse than childbirth. The protozoan caused vomiting and watery diarrhea as well.
To become so nastily infected, a person must swallow oocysts, the tough capsules that shelter the infectious form of the parasite. When stomach acid dissolves the oocysts’ coating, the parasites are released into the gut, where they infect cells, multiply, and form more oocysts. A few days later they are shed in diarrhea.
Since Cyclospora was first identified in 1977, it has been implicated in just three small waterborne outbreaks in this country, all within the last six years. Because the microbe is so rare and difficult to culture, most laboratories don’t check for it even when food poisoning is suspected. Moreover, the weeklong lag between infection and symptoms is long enough for people to forget what they’ve eaten.
Still, investigators from the Centers for Disease Control and Prevention in Atlanta managed to identify a probable source of the 1996 outbreak: Guatemalan raspberries, which either had been or could have been served at half of the 42 events health officials examined. Cyclospora was never found on any berries here or in Guatemala, though, nor did the parasite turn up in samples of the water, soil, or stools of agricultural workers in Guatemala. But since current screening tests are unreliable, says cdc epidemiologist Barbara Herwaldt, the fact that we didn’t find it doesn’t mean it wasn’t there. There’s a lot that remains to be learned about this organism, including which foods it is most likely to contaminate and whether washing them does much good.