Outbreak of Cyclosporiasis -- Ontario, Canada, May 1998

During May-June 1998, the Ontario Ministry of Health and local health departments in Ontario received reports of clusters of cases of cyclosporiasis associated with events held during May. This report describes the preliminary findings of the investigation of a cluster in Toronto, Ontario, and summarizes the findings from investigations of 12 other clusters. These investigations indicated that fresh raspberries imported from Guatemala were linked to the multicluster outbreak.

Toronto, Ontario

On June 2, Toronto Public Health was notified of a laboratory-confirmed case of cyclosporiasis in a person who attended a dinner at a hotel in Toronto on May 8. Six other persons who attended the dinner were reported to have diarrheal illness. A case of cyclosporiasis was defined as onset of any gastrointestinal (e.g., nausea or vomiting) or constitutional (e.g., fever or fatigue) symptom 1-14 days after the dinner and either 1) laboratory confirmation of Cyclospora oocysts in a stool specimen; 2) diarrhea (i.e., three or more loose or watery stools during a 24-hour period); or 3) at least four gastrointestinal symptoms. Of the 174 persons who attended the dinner, 128 (74%) were interviewed. Of these 128 persons, 29 (23%) had illness that met the case definition; three of the 29 persons had laboratory-confirmed cyclosporiasis. The median incubation period was 8 days (range: 1-12 days). All 29 case-patients had diarrhea; the median duration of diarrheal illness was 7 days (range: 1-34 days).

Eating the berry garnish (which included raspberries, blackberries, strawberries, and possibly blueberries) for the dessert was significantly associated with risk for illness. Of the 108 persons who ate or probably ate the berry garnish, 28 (26%) became ill, compared with one (5%) of the 20 persons who did not or probably did not eat the berry garnish (relative risk {RR}=5.2; p=0.04, Fisher's exact test). Among the berries in the garnish, raspberries were the only berries significantly associated with risk for illness. Of the 94 persons who ate or probably ate the raspberries, 27 (29%) became ill, compared with two (6%) of the 32 persons who did not or probably did not eat the raspberries (RR=4.6; 95% confidence interval=1.2-18.3).

Other Investigations

Twelve other clusters of cases of cyclosporiasis in addition to the Toronto cluster described above have been investigated; each of the 13 clusters had two or more cases, at least one of which was laboratory confirmed. Based on preliminary data, the 13 clusters comprise 192 cases; 46 (24%) of the 192 were laboratory confirmed. The dates of the events associated with the clusters ranged from May 2 through May 23, 1998.

Fresh raspberries were the only food in common to all 13 events. Raspberries were included in mixtures of various types of berries at 12 events and were the only type of berry served at one event. The median of the event-specific attack rates for the 13 events, irrespective of exposures, was 89% (range: 23%-100%). The median of the event-specific attack rates for persons who ate or probably ate the food items that included raspberries was 100% (range: 26%-100%); the median attack rate for persons who did not or probably did not eat these food items was 0% (range: 0%-67%). Eating the food items that included raspberries was significantly associated with risk for illness for five events; for the other eight events, eating the raspberry-containing food items could account for 60 (92%) of 65 cases. Traceback investigations to identify the source(s) of the raspberries have been completed for eight events, including the event described above; Guatemala was the only source of the raspberries served at the events. Mesclun lettuce and fresh basil, which were implicated in outbreaks of cyclosporiasis in the United States in 1997 (1,2), each were served at two events but were not significantly associated with risk for illness.

Reported by: Toronto Public Health, Toronto; Haliburton-Kawartha-Pine Ridge District Health Unit, Port Hope; Simcoe County District Health Unit, Barrie; York Regional Health Unit, Newmarket; Disease Control Svc, Public Health Br, Ontario Ministry of Health, Toronto; Central Public Health Laboratory, Laboratory Services Br, Ontario Ministry of Health, Toronto. Canadian Food Inspection Agency, Fresh and Processed Plant Products Div, Ottawa, and Food Inspection, Ontario Region, Toronto and Guelph; Bur of Infectious Diseases and Field Epidemiology Training Program, Laboratory Center for Disease Control, and Food Directorate, Health Canada, Ottawa. Parasitic Disease Surveillance Unit, New York City Dept of Health, New York. Div of Parasitic Diseases, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note

Editorial Note: The findings in this report indicate that fresh raspberries imported from Guatemala were linked to the outbreak of cyclosporiasis in Ontario in May 1998. Outbreaks of cyclosporiasis in North America in the spring of 1996 and 1997 also were linked to Guatemalan raspberries; the mode of contamination of the raspberries was not identified for any of these outbreaks (1,3). No outbreaks were recognized in association with Guatemalan raspberries during Guatemala's fall and winter export seasons in 1996 and 1997.

After the outbreak in 1996, berry growers and exporters in Guatemala, in consultation with the Food and Drug Administration (FDA) and CDC, voluntarily introduced control measures that focused on improving water quality and sanitary conditions on individual farms (1). In the spring of 1997, another outbreak of cyclosporiasis occurred despite the implementation of control measures and the restriction (beginning April 22, 1997) that, during that spring, only farms classified by the Guatemalans as low risk could export to North America (1). In the spring of 1998, FDA did not allow importation of fresh raspberries from Guatemala into the United States. The Canadian Food Inspection Agency reported that fresh raspberries from farms that the Guatemalans had classified as low risk continued to be imported into Canada until June 9, 1998. The occurrence of outbreaks in 1997 and 1998 despite the implementation of control measures on Guatemalan farms suggests either that the control measures may not have been fully implemented by some farms, were not effective, or were not directed against the true source of contamination of the raspberries (1). The Guatemalan Berry Commission and the government of Guatemala are developing a more comprehensive plan for growing and handling raspberries that includes additional control measures and inspection criteria; the plan is being reviewed by U.S. and Canadian officials.

This is at least the third, and possibly the fourth (4), consecutive year in which outbreaks of cyclosporiasis linked to consumption of raw produce have occurred in North America. In addition to Guatemalan raspberries, fresh mesclun lettuce and fresh basil that were not from Guatemala have been implicated in outbreaks in the United States (1,2). The mode of contamination of the produce was not determined for any of the outbreaks, in part because the methods for detecting Cyclospora on produce and in other environmental samples are insensitive for detecting low levels of the parasite. Produce should be washed thoroughly before it is eaten; however, this practice does not eliminate the risk for transmission of Cyclospora (3,5,6).

Health-care providers should consider the diagnosis of Cyclospora infection in persons with prolonged diarrheal illness and specifically request testing of stool specimens for this parasite. The average incubation period for cyclosporiasis is 1 week; in patients who are not treated with trimethoprim-sulfamethoxazole (7), illness can be protracted, with remitting and relapsing symptoms.

Cases of Cyclospora infection unrelated to travel outside of Canada or the United States may be associated with a new outbreak. Newly identified clusters should be investigated to identify the vehicles of infection and to identify the sources and modes of contamination of the implicated vehicles. Although cyclosporiasis is not a reportable disease in any Canadian province or territory, as of June 1998, five states and one municipality in the United States had mandated reporting. In June 1998, the Council of State and Territorial Epidemiologists passed a resolution recommending that cyclosporiasis be made a nationally notifiable disease in the United States. In jurisdictions where formal reporting mechanisms are not yet established, clinicians and laboratorians who identify cases of cyclosporiasis unrelated to travel outside North America are encouraged to inform the appropriate local, provincial, territorial, or state health departments, which in turn are encouraged to contact, in Canada, the Division of Disease Surveillance, Bureau of Infectious Diseases, Laboratory Center for Disease Control, telephone (613) 941-1288; and, in the United States, CDC's Division of Parasitic Diseases, National Center for Infectious Diseases, telephone (770) 488-7760.

References

1. CDC. Update: outbreaks of cyclosporiasis -- United States and Canada, 1997. MMWR 1997;46:521-3.

2. CDC. Outbreak of cyclosporiasis -- Northern Virginia-Washington, D.C.-Baltimore, Maryland, Metropolitan Area, 1997. MMWR 1997;46:689-91.

3. Herwaldt BL, Ackers M-L, Cyclospora Working Group. An outbreak in 1996 of cyclosporiasis associated with imported raspberries. N Engl J Med 1997;336:1548-56.

4. Koumans EH, Katz DJ, Malecki JM, et al. An outbreak of cyclosporiasis in Florida in 1995: a harbinger of multistate outbreaks in 1996 and 1997. Am J Trop Hyg 1998;59:235-42.

5. Robbins JA, Sjulin TM. Scanning electron microscope analysis of drupelet morphology of red raspberry and related Rubus genotypes. Journal of the American Society of Horticultural Science 1988;113: 474-80.

6. Ortega YR, Roxas CR, Gilman RH, et al. Isolation of Cryptosporidium parvum and Cyclospora cayetanensis from vegetables collected in markets of an endemic region in Peru. Am J Trop Med Hyg 1997;57:683-6.

7. 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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