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The Return of Cyclospora in 1997: Another Outbreak of Cyclosporiasis in North America Associated with Imported Raspberries

Barbara L. Herwaldt, MD, MPH; Michael J. Beach, PhD, the Cyclospora Working Group*
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From the Centers for Disease Control and Prevention, Atlanta, Georgia.

Ann Intern Med. 1999;130(3):210-220. doi:10.7326/0003-4819-130-3-199902020-00006
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Background: In the spring of 1996, an outbreak of cyclosporiasis associated with fresh Guatemalan raspberries occurred in the United States and Canada. Another multistate outbreak of cyclosporiasis occurred in North America in the spring of 1997.

Objective: To identify the vehicle of the outbreak that occurred in the spring of 1997.

Design: Retrospective cohort studies of clusters of cases associated with events (such as banquets) and traceback investigations of sources of implicated produce.

Setting: United States and Canada.

Patients: Persons who attended events associated with clusters of cases of cyclosporiasis.

Measurements: Identification of clinically defined or laboratory-confirmed cases of cyclosporiasis and risk factors for infection.

Results: 41 clusters of cases were reported in association with events held from 1 April through 26 May in 13 U.S. states, the District of Columbia, and 1 Canadian province. The clusters comprised 762 cases of cyclosporiasis, 192 (25.2%) of which were laboratory confirmed. In addition, 250 laboratory-confirmed sporadic cases were reported in persons who developed gastrointestinal symptoms from April through 15 June, for a total of 1012 cases. Fresh raspberries were the only food common to all 41 events and were the only type of berry served at 9 events (22.0%). Statistically significant associations between consumption of raspberry-containing items and cyclosporiasis were documented for 15 events (40.5% of 37). For 31 of the 33 events with well-documented traceback data, the raspberries either definitely came from Guatemala (8 events) or could have come from Guatemala (23 events). The mode of contamination of the raspberries remains unknown. The outbreak ended shortly after the exportation of fresh raspberries from Guatemala was voluntarily suspended at the end of May 1997.

Conclusions: Similar multistate, multicluster outbreaks of cyclosporiasis associated with consumption of Guatemalan raspberries have occurred in consecutive years. These outbreaks highlight the need for better understanding of the biology and epidemiology of Cyclospora cayetanensis and for stronger prevention and control measures to ensure the safety of produce eaten raw.

*For a list of the members of the Cyclospora Working Group, see the Appendix.


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Figure 1.
Top. Dates of 41 events associated with clusters of cases of cyclosporiasis (n= 762 cases) in the United States and Canada in April and May 1997.Bottom. Dates of symptom onset for laboratory-confirmed sporadic cases of cyclosporiasis in the United States and Canada in 1997.

For multiday events, the date of the first day of the event is shown. The last shipment of Guatemalan raspberries in the spring of 1997 was on 28 May. The white bars represent 31 case-patients who became ill during the period from March through August but not during the outbreak period of April through 15 June. The black bars represent 250 case-patients whose cases were classified as having occurred during the outbreak period. The median date of symptom onset for the 250 case-patients was 26 May (range, 6 April to 15 June). Only 22 persons (8.8%) became ill in April, and most (225 [90.0%]) became ill by 4 June. The date selected as the last date of the outbreak period was 15 June because Guatemalan raspberries exported in late May could still have been available for consumption in early June and because infected persons would have become symptomatic an average of 1 week after exposure. Not all of the sporadic cases of cyclosporiasis were necessarily due to consumption of raspberries.

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Figure 2.
Tracebacks of sources of raspberries served at events associated with clusters of cases of cyclosporiasis in North America in 1997.†

*Includes three events (one traced to Guatemalan exporter A and two traced to Guatemalan exporter B) for which there might have been additional branches of the tracebacks without well-documented data; only well-documented data are included here. A farm was considered linked to an event if it contributed to a shipment of raspberries that could have been used at that event.

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Figure 3.
Sources and amounts of fresh raspberries (domestic and imported) shipped within the United States by week for 9 weeks in April and May 1996 (left) and 1997 (right).

The white bars represent raspberries from California; the striped bars represent raspberries from Chile; the black bars represent raspberries from Guatemala; and the dotted bars represent raspberries from other sources. The dates for weeks 1 through 9 range from 31 March 1996 to 1 June 1996 and from 30 March 1997 to 31 May 1997; the last date in each week is shown under each bar. Data on Chilean raspberries were unavailable for week 1 in 1997. The median proportions of the raspberries per week that were from Guatemala were 13.8% (range, 0% to 21.9%) in 1996 and 11.0% (range, 2.8% to 18.4%) in 1997 (excluding week 1).

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