Was Romaine to Blame for a 2013 Multistate Cyclosporiasis Outbreak? Revisiting John Snow's Method for Answers

Monday, June 23, 2014: 11:06 AM
103, Nashville Convention Center
Bryan Buss , Nebraska Department of Health and Human Services, Lincoln, NE
Manjiri Joshi , Nebraska Department of Health and Human Services, Lincoln, NE
Jamie DeMent , Florida Department of Health, Tallahassee, FL
Venessa Cantu , Texas Department of State Health Services, Austin, TX
Thomas Safranek , Nebraska Department of Health and Human Services, Lincoln, NE

BACKGROUND: During June–August 2013, 25 states reported 631 cyclosporiasis cases including Nebraska [n=87] and Iowa [n=140] where a regional collaborative investigation identified Producer A-, Distributor X-bagged–salad mix (Lot T) as the likely source of illnesses associated with Chain A/B restaurants (both corporately owned by one company). Given these findings, we convened a multistate investigation to identify ill persons who might have consumed common-source products in Chains A/B or elsewhere, and define national distribution for persons with illness onsets during a commensurate timeframe. 

METHODS: Using Producer A-, Distributor X-provided data, we conducted distribution-level analyses to identify source-growing field(s) for four salad-mix ingredients stratifying by lot code. Producer A subsequently provided grower-specific US product distribution information to investigate common-source exposures and to compare national distribution of ill persons to locations of lot- and grower-specific salad-item shipments.  

RESULTS: From June 2–6, 3,262 Producer A bagged-salad mix cases were shipped to five Distributor X centers in Nebraska, Iowa, and neighboring states; four distributed 424 Lot T cases to 25 Chain A/B restaurants where 170 ill persons reported exposure. Elsewhere, 263 Lot T salad-mix cases were distributed, including 168 to Florida Distributor P; Chain A/B delivery included Lot T shipments to two restaurants each respectively patronized by 2 salad-consuming confirmed-ill persons. Upon November 4 receipt of Producer A trace-forward information, a romaine-only lettuce product also designated as Lot T (Grower/Ranch Lot R) was supplied by one Texas distributor to 3 Chain C restaurants each patronized by 3 separate salad-consuming, confirmed-ill persons. In Florida, approximately 14,000 pounds of Grower/Lot R romaine was received by four distributors for Chain A/B delivery among which 5 confirmed-ill persons reported dining. Nationwide, approximately 67,000 pounds of Grower/Lot R romaine was shipped June 2–6 by Producer A to 27 distributors in 17 central and eastern states. In these regions, 336 confirmed-ill persons with June 7–July 1 illness onset where identified of whom 97% (327/336) resided in states with known Grower/Lot R romaine distribution; 3% (9/336) resided in immediately adjacent states.  

CONCLUSIONS: Our findings demonstrate that Producer A-distributed, single grower/ranch lot romaine lettuce was served at Chain A/B (Nebraska, Iowa, Wisconsin, and Florida) and C (Texas) restaurants reported by 177 and 3 confirmed-ill persons, respectively. Further, we suggest common-origin Grower/Lot R romaine as a likely source for most June 7–July 1 onset illnesses nationwide. Grower R’s production practices should be investigated to determine potential contamination sources and develop prevention recommendations.