NEW YORK Investigators continue to look for the source of a protozoan parasite that has caused outbreaks of intestinal illness in the United States and Canada.
Investigators have traced contaminated food items to Guatemala but they do not know how contamination had occurred, said Barbara Herwaldt, MD, a medical epidemiologist with the Centers for Disease Control and Prevention (CDC).
The parasite is called Cyclospora cayetanensis and more than 850 laboratory confirmed cases of C. cayetanensis illness had been reported in the United States and Canada by July 15. Many cases occurred in clusters, according to Herwaldt.
"Although we're focusing on raspberries, we're not ruling out the possibility that other berries may be involved," Herwaldt said.
The Food and Drug Administration (FDA) is testing various foods "that have come into question" as possible sources of the parasite, said FDA spokesperson Brad Stone. To facilitate identification of the food or foods responsible for the outbreaks, the FDA has developed a faster and more efficient method to test foods for Cyclospora, Stone said.
Cyclospora infection causes an illness that can persist for weeks if untreated. The illness is characterized by watery diarrhea, nausea, abdominal cramping, vomiting and loss of appetite. Diarrhea and other symptoms may subside and then return. The illness, which can be treated with trimethoprim-sulfamethoxazole, is rarely fatal.
Following exposure to the parasite, symptoms of the illness typically do not appear for about a week, a relatively long incubation period that exceeds that of most common bacterial and viral causes of diarrhea, Herwaldt said. The lengthy incubation period can be an important clue for identifying cases of Cyclospora infection, but it also may impair the ability of people to recall how they were exposed to the parasite.
Early on, investigators had implicated strawberries as the parasite's source in some cases. Health officials in Houston, which had 62 confirmed cases of Cyclospora related illness, initially advised people not to eat fresh strawberries "until more information is available about their safety." The officials eventually had lifted that advisory, and they had expanded their investigation to include "the world of berries," said Kathy Barton, a spokesperson for the Houston Department of Health and Human Services.
Outbreaks of Cyclospora illness also had been reported in Dallas and Austin, said Lynn Denton, a spokesperson for the Texas Department of Health.
During an outbreak of Cyclospora illness in metropolitan Toronto, Ontario's chief medical officer, Richard Schabas, MD, had advised the public to wash U.S.-grown strawberries thoroughly before eating them. Health officials eventually expanded that advisory to include all imported berries.
In New York City, which had more than 100 confirmed cases of Cyclospora illness, health department commissioner Margaret A. Hamburg, MD, had stated on June 26 that the department had "sufficient information to link most of the cases here to either eating fresh strawberries or raspberries or both."
Three New York City residents with underlying illnesses had been hospitalized because of diarrhea-related dehydration.
Raspberries also surfaced as a suspect in South Carolina. Cyclospora-associated diarrhea occurred among 37 of 64 people who had attended a luncheon at an establishment near Charleston, S.C., on May 23. Raspberries were the food most strongly associated with illness, followed by strawberries and potato salad. At the same establishment on the same day, 95 people had attended another gathering and were served strawberries obtained from the same source, but were not served raspberries. Investigators identified no cases of Cyclospora infection among this second group.
Little is known about Cyclospora which investigators first identified as a cause of human illness in 1977. Prior to the recent series of outbreaks, three documented outbreaks of Cyclospora illness had occurred in the United States. The first occurred among physicians and others who worked at a Chicago hospital in 1990. Investigators suspect that people acquired the pathogen by drinking water that had been in a water-storage tank serving a physician dormitory at the hospital.
Cyclospora joins a growing list of microbes that health officials in recent years have come to recognize as important causes of diarrhea outbreaks. These microbes include Cryptosporidium parvum and Escherichia coli O157:H7
For more information, see:
- Huang P, Weber JT, So sin DM, et al. The first reported outbreak of diarrheal illness associated with Cyclosporain the United States. Ann Intern Med. 1995; 123:401-14.
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