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Outbreak of Cyclosporiasis -- Northern Virginia-Washington, D.C.-Baltimore, Maryland, Metropolitan Area, 1997

During July 1997, state and local health departments in Virginia, the District of Columbia (DC), and Maryland received reports of clusters of cases of cyclosporiasis associated with events (e.g., luncheons) held in their jurisdictions during June and July. This report describes the preliminary findings of the investigation of a cluster in Virginia and summarizes the findings from ongoing investigations of the other clusters. Fresh basil has been implicated as the probable vehicle of infection. Alexandria, Virginia

On July 7, a company physician reported to the Alexandria Department of Health (ADOH) that most of the employees who attended a corporate luncheon on June 26 at the company's branch in Fairfax, Virginia, had developed gastrointestinal illness. The luncheon was catered by the Alexandria branch of company A. Company A operates nine stores in the northern Virginia-DC-Baltimore, Maryland, metropolitan area: a central production kitchen and retail food store in Bethesda, Maryland; and eight branch stores, each with a kitchen and retail store.

On July 11, the health department was notified that a stool specimen from one of the employees who attended the luncheon was positive for Cyclospora oocysts. A clinical case of cyclosporiasis was defined as onset of at least four gastrointestinal symptoms, such as diarrhea, nausea, vomiting, or abdominal cramps, 1-14 days after the luncheon. All 54 persons who attended the luncheon on June 26 or who ate leftover food on June 27 were interviewed. Of the 54 persons, 48 (89%) had illness that met the clinical case definition, including 17 whose infections were laboratory confirmed by examination of stool specimens. The median incubation period was 8 days (range: 3-12 days). Of the 48 case-patients, 45 had diarrhea (three or more loose stools during a 24-hour period), with a median number of stools per day of seven (range: three to 35 stools) and a median duration of diarrheal illness of 5 days (range: 1-10 days).

Eating the basil-pesto pasta salad, which was served cold, was the only exposure significantly associated with risk for illness in univariate analysis; 43 (98%) of the 44 persons who ate this food item became ill, compared with one (17%) of six persons who did not eat it (relative risk=5.9; p less than 0.001, Fisher's exact test; four ill persons did not recall whether they had eaten the salad). The one ill person who did not eat the salad used the spoon from the salad to serve himself leftovers of another food item that he ate on June 27. The salad had been prepared in the Alexandria store with basil-pesto sauce made in the production kitchen in Bethesda. No raspberries or mesclun lettuce, which caused outbreaks of cyclosporiasis in the United States this spring (1), were served at the luncheon. Other Investigations

Twenty-five clusters of cases of cyclosporiasis with at least one laboratory-confirmed case per cluster (i.e., confirmed clusters) have been reported in association with events held in the northern Virginia-DC-Baltimore metropolitan area during June and July. In addition, at least 20 possible clusters for which laboratory confirmation has not yet been obtained have been reported. The dates of the events associated with confirmed and possible clusters ranged from June 16 to July 8 and from June 15 to July 12, respectively. Based on preliminary interview data, the 25 confirmed clusters comprise approximately 185 cases (approximately 60 laboratory-confirmed and 125 clinically defined cases), and the 20 possible clusters, approximately 75 clinically defined cases.

All 25 confirmed clusters were associated with events at which at least one food item that contained fresh basil from company A was served (i.e., fresh basil or a prepared food item that contained fresh basil was either purchased at one of its retail stores or served at a meal prepared in one of its kitchens). Six of the nine company A stores have been linked to clusters. For 23 of the 25 events, a basil-containing item that included basil-pesto sauce (e.g., in a pasta salad or on a sandwich) made at the Bethesda store was served. Company A reported that its practice was to wash basil that it used to make pesto sauce. Eating the food item that contained basil was significantly associated (p less than 0.05) or associated (i.e., all ill persons had eaten the item but the p value was greater than or equal to 0.05) with risk for illness for all six events for which preliminary epidemiologic data are available.

At the direction of the ADOH, on July 12, company A terminated production and sales of pesto sauce made with fresh basil and of food items that contained this sauce and terminated sales of fresh basil. On July 18, health departments in Virginia and Maryland issued press releases to inform the public not to consume fresh basil or fresh basil-containing food items previously purchased from company A. State and local health departments, CDC, and the Food and Drug Administration (FDA) are continuing investigations to determine the sources and distribution of the basil; to determine how basil is handled, processed, and distributed by company A; and to identify modes of contamination. FDA and CDC are testing for the presence of Cyclospora oocysts in samples of fresh basil and basil-pesto sauce obtained in mid-July from company A and in leftover pesto sauce obtained from several ill persons.

Reported by: R Pritchett, MPH, C Gossman, V Radke, MPH, J Moore, MHSA, E Busenlehner, K Fischer, K Doerr, C Winkler, M Franklin-Thomsen, J Fiander, J Crowley, E Peoples, L Bremby, J Southard, MSN, L Appleton, D Bowers, MSN, J Lipsman, MD, Alexandria Dept of Health, Alexandria; H Callaway, D Lawrence, R Gardner, Fairfax Dept of Health, Fairfax; B Cunanan, R Snaman, Arlington Dept of Health, Arlington; J Rullan, MD, G Miller, Jr, MD, State Epidemiologist, Virginia Dept of Health; S Henderson, M Mismas, T York, PhD, J Pearson, PhD, Div of Consolidated Svcs, Commonwealth of Virginia. C Lacey, J Purvis, N Curtis, K Mallet, Montgomery County Health Dept, Rockville; R Thompson, Baltimore County Health Dept, Towson; D Portesi, MPH, DM Dwyer, MD, State Epidemiologist, Maryland Dept of Health and Mental Hygiene. M Fletcher, PhD, M Levy, MD, District Epidemiologist, District of Columbia Dept of Health. T Lawford, MD, Fairfax, Virginia. M Sabat, MS, Chicago, Illinois. M Kahn, Atlanta, Georgia. Office of Regulatory Affairs, and Center for Food Safety and Applied Nutrition, Food and Drug Administration. Div of Parasitic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The preliminary findings of the investigations described in this report implicate fresh basil from company A as the probable vehicle of infection for the clusters of cases of cyclosporiasis recently identified in the northern Virginia-DC-Baltimore metropolitan area. To date, all of these clusters have been associated with company A, even though the produce distributor that was the sole supplier for company A during the relevant period provided a large (as yet undetermined) proportion of its inventory of fresh basil to other local establishments. Some of the implicated food items from company A did not contain basil-pesto sauce; therefore, basil, rather than the other ingredients of the pesto sauce, is the probable vehicle. The mode of contamination of the basil is being investigated. Cyclospora oocysts are not infectious (i.e., are unsporulated) at the time of excretion. However, the minimum time required for sporulation is unknown, and the conditions in the environment and in foods that expedite sporulation are poorly understood.

In addition to the cases of cyclosporiasis associated with consumption of basil, approximately 1450 other cases of cyclosporiasis, approximately 550 of which have been laboratory confirmed, have been reported in the United States and Canada in 1997. Fresh raspberries imported from Guatemala and mesclun lettuce (specific source not yet determined) have both been implicated as vehicles of infection in outbreak investigations in 1997 (1). The implication of three different vehicles of infection during 1997 highlights the need for strengthened prevention and control measures to ensure the safety of produce that is eaten raw and the need for improved understanding of the epidemiology of Cyclospora.

The average incubation period for cyclosporiasis is 1 week; in patients who are not treated with trimethoprim-sulfamethoxazole (2), illness can be protracted, with remitting and relapsing symptoms. 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 cyclosporiasis should contact CDC's Division of Parasitic Diseases, National Center for Infectious Diseases, telephone (770) 488-7760. Newly identified clusters should be investigated to identify the vehicles of infection and to identify the sources and modes of contamination of implicated foods.


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

  2. 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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