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Outbreaks of Cyclospora cayetanensis Infection -- United States, 1996

Cyclospora cayetanensis (previously termed cyanobacterium-like body) is a recently characterized coccidian parasite (1); the first known cases of infection in humans were diagnosed in 1977 (2). Before 1996, only three outbreaks of Cyclospora infection had been reported in the United States (3-5). This report describes the preliminary findings of an ongoing outbreak investigation by the South Carolina Department of Health and Environmental Control (SCDHEC) and summarizes the findings from investigations in other states. South Carolina

On June 14, the SCDHEC was notified of diarrheal illness among persons who attended a luncheon near Charleston on May 23. A case of Cyclospora infection was defined as diarrhea (three or more loose stools per day or two or more stools per day if using antimotility drugs) after attending the luncheon. All 64 attendees were interviewed. Of the 64 persons, 37 (58%) had Cyclospora infection, including seven with laboratory-confirmed infection. The median incubation period was 7.5 days (range: 1-23 days).

Based on univariate analysis by the SCDHEC, food items associated with illness included raspberries (RR=5.6; 95% CI=2.3-13.7), strawberries (RR=2.2; 95% CI=1.0-5.1), and potato salad (RR=1.9; 95% CI=1.3-2.7). On May 23, a total of 95 persons attended a luncheon in an adjacent room and were served strawberries obtained from the same source but were not served raspberries; no cases were identified among these persons. One person who ate raspberries at the establishment that evening developed laboratory-confirmed infection; she had not attended either luncheon or eaten strawberries. Other investigations

In May and June 1996, social event-related clusters of cases and/or sporadic cases of Cyclospora infection were reported in at least 10 states and in Ontario, Canada. Several hundred laboratory-confirmed cases have been reported to CDC. Most cases have occurred in immunocompetent adults.

Preliminary evidence suggests that, in these outbreaks, consumption of fresh fruit -- raspberries and mixtures of berries and other fruits (precluding determination of which fruit in the mixture was associated with illness) -- may be associated with Cyclospora infection. CDC, the Food and Drug Administration (FDA), and health officials in state and local health departments and Canada are collaborating to determine the extent and causes of the outbreaks, the sources of contamination, and whether transmission is ongoing. Additional efforts include the use of the five-site CDC/U.S. Department of Agriculture/FDA active foodborne diseases surveillance network (established in 1995; collaborating sites include Atlanta and portions of California, Connecticut, Minnesota, and Oregon). Although standardized methods are not yet available, FDA, CDC, and others are testing samples of produce for Cyclospora.

Reported by: J Chambers, MD, S Somerfeldt, MS, L Mackey, S Nichols, MS, Trident Health District; R Ball, MD, D Roberts, MPH, N Dufford, MS, A Reddick, PhD, J Gibson, MD, State Epidemiologist, South Carolina Dept of Health and Environmental Control. Center for Food Safety and Applied Nutrition, and Office of Regulatory Affairs, Food and Drug Administration. Div of Field Epidemiology, Epidemiology Program Office; Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, and Epidemiology Br, Div of Parasitic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Although Cyclospora is transmitted by the fecal-oral route, direct person-to-person transmission is unlikely because excreted oocysts require days to weeks under favorable environmental conditions to become infectious (i.e., sporulate). Whether animals serve as sources of infection for humans is unknown. Most reported cases have occurred during spring and summer. The average incubation period is 1 week, and illness may be protracted (from days to weeks) with frequent, watery stools and other gastrointestinal symptoms; symptoms may remit and relapse.

The diameter of Cyclospora oocysts is 8-10 um, approximately twice that of Cryptosporidium parvum. Oocysts can be identified in stool by examination of wet mounts under phase microscopy, use of modified acid-fast stains (oocysts are variably acid-fast), or demonstration of autofluorescence with ultraviolet epifluorescence microscopy. However, these procedures are not routine for most clinical laboratories, and confirmation of the diagnosis by an experienced reference laboratory is recommended. Demonstration of sporulation provides definitive evidence for the diagnosis (1). Infection with Cyclospora can be treated with a 7-day course of oral trimethoprim (TMP)-sulfamethoxazole (SMX) (for adults, TMP 160 mg plus SMX 800 mg twice daily; for children, TMP 5 mg/kg plus SMX 25 mg/kg twice daily) (6). Treatment regimens for patients who cannot tolerate sulfa drugs have not yet been identified.

The preliminary findings of these investigations suggest that consumption of some fresh fruits has been associated with increased risk for illness. However, the investigations have not yet determined specific sources or modes of contamination. Potential sources of infection include seasonal produce that orginates from different domestic and international locations at different times of the year; the complex distribution routes and handling of these foods complicate tracebacks and other key aspects of the investgations. As always, produce to be eaten raw should be thoroughly washed. This practice may not entirely eliminate the risk of transmission of Cyclospora. Health-care providers should consider Cyclospora infection in persons with prolonged diarrheal illness and specifically request laboratory testing for this parasite; cases should be reported to local and state health departments. Health departments that identify cases of Cyclospora infection should contact CDC's Division of Parasitic Diseases, National Center for Infectious Diseases, telephone (770) 488-7760.


  1. Ortega YR, Sterling CR, Gilman RH, Cama VA, Daz F. Cyclospora species -- a new protozoan pathogen of humans. N Engl J Med 1993;328:1308-12.

  2. Ashford RW. Occurrence of an undescribed coccidian in man in Papua New Guinea. Ann Trop Med Parasitol 1979;73:497-500.

  3. Huang P, Weber JT, Sosin DM, et al. The first reported outbreak of diarrheal illness associated with Cyclospora in the United States. Ann Intern Med 1995;123:409-14.

  4. Carter RJ, Guido F, Jacquette G, Rapoport M. Outbreak of cyclosporiasis at a country club -- New York, 1995 {Abstract}. In: 45th Annual Epidemic Intelligence Service (EIS) Conference. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, April 1996:58.

  5. Koumans EH, Katz D, Malecki J, et al. Novel parasite and mode of transmission: Cyclospora infection -- Florida {Abstract}. In: 45th Annual Epidemic Intelligence Service (EIS) Conference. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, April 1996:60.

  6. Hoge CW, Shlim DR, Ghimire M, et al. Placebo-controlled trial of co-trimoxazole for cyclospora infections among travellers and foreign residents in Nepal. Lancet 1995;345:691-3.

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