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BACKGROUND: During June—August 2013, a multistate outbreak including 631 cyclosporiasis cases was reported to CDC. Most cases occurred in Iowa (140), Nebraska (87), and Texas (270). In Iowa and Nebraska, most illness onsets occurred during June, and were associated with consumption of pre-packaged salad mix containing lettuce, cabbage, and carrots. Most Texas patients had illness onsets during July. These temporal differences suggested that a different food vehicle might be causing illnesses in Texas. State health department-administered questionnaires identified multiple Texas clusters: of the two largest, Cluster 1 comprised patients from a small town (Town X), and Cluster 2 included patients who ate at a single restaurant (Restaurant A) in a different town during the incubation period. We investigated these clusters to identify possible additional contaminated food vehicles.
METHODS: Cases were defined as gastrointestinal illness in persons between June 1-August 31, 2013 with Cyclospora in stool and without international travel ≤2 weeks before illness onset. We interviewed Cluster 1 case-patients about foods eaten ≤14 days before illness onset and compared results with 2006–2007 New Mexico Foodborne Diseases Active Surveillance Network (FoodNet) Population Survey data. We conducted a case-control study with Cluster 2, including case-patients who ate at Restaurant A during July 6–16, 2013, and Restaurant A meal date-matched controls reporting no diarrhea ≤14 days afterwards. Menu-specific questionnaires were administered to gather meal consumption data and ingredient-level analyses were performed.
RESULTS: The seven Cluster 1 patients were significantly more likely to have consumed fresh cilantro (odds ratio [OR]:18.7; 95% confidence interval [CI]:2.2-863.4) and lemon (OR:11.2; 95% CI: 1.4-516.9) than FoodNet respondents. We interviewed 21 Cluster 2 case-patients and 65 controls. Eating fresh cilantro (matched OR [mOR]:19.8; CI:4.0–>999), onions (mOR:15.3; CI:2.1-697.7), and tomatoes (mOR:5.5; CI:1.1-54.1) from Restaurant A was significantly associated with illness. Of these, only cilantro was consumed by all Cluster 2 case-patients. Additionally, of the four salsas prepared at Restaurant A, three containing uncooked cilantro were significantly associated with illness (hot salsa mOR:8.0; CI:2.3-31.4; side salsa mOR:5.7; CI:1.6-23.7; fire salsa mOR:3.5; CI:1.1-12.7), while salsa containing cooked cilantro was not (salsa ranchera mOR:6.0; CI:0.7-75.2).
CONCLUSIONS: Cilantro was the likely source of illnesses among patients in Texas Cluster 2. Although these illnesses occurred soon after identification of a multistate outbreak linked to pre-packaged salad mix, these investigations indicate that the large increase in cyclosporiasis illnesses during summer 2013 were caused by at least two different food vehicles.