Partnering with Industry in a Multi-State Outbreak Investigation of Shiga Toxin-Producing E. Coli O157:H7

BACKGROUND:  Shiga Toxin-producing E. coli (STEC) O157:H7 is a nationally notifiable gastrointestinal illness. During 2012, Utah experienced a statewide outbreak of STEC O157:H7 with 13 confirmed cases. Onset dates ranged from June 29 to August 24, with the majority (77%) occurring in August. Illness in Utah was associated with two locations of Mexican-style Restaurant Chain A; nineteen other states reported matching Pulsed-Field Gel Electrophoresis (PFGE) patterns. The Utah Department of Health (UDOH) led the investigation in collaboration with federal, state, local, and industry partners.

METHODS:  UDOH was alerted by Unified State Laboratories: Public Health of five cases indistinguishable by two-enzyme PFGE. Hypothesis generation included industry engagement to complete a Restaurant A ingredient commonality evaluation, binomial comparison of exposure data, targeted interviewing through electronic questionnaires, and traceback initiation.  Further investigation was led by: comparison of Utah and non-Utah case information, analysis of electronically self-reported data by previously non-responsive cases, and utilization of Multiple-Locus Variable Analysis (MLVA) to eliminate non-outbreak associated cases.

RESULTS:  Collaboration with industry facilitated a meal comparison for Restaurant A associated cases, identifying cilantro and romaine as common ingredients. Binomial comparison of exposure data gathered through targeted interviewing (67% response rate) identified romaine lettuce as a suspect vehicle and cilantro was not statistically significant, p-values (0.0001) and (0.6) respectively.   Self-reported electronic surveys supplemented exposure data through inclusion of cases that were previously non-responsive. Traceback efforts flagged romaine lettuce early and converged on a California brand. Seven environmental isolates indistinguishable by PFGE and MLVA were previously reported in California. No environmental samples were collected from Restaurant A locations or romaine lettuce fields. MLVA ruled out ten non-outbreak cases and directed further targeted interviewing.

CONCLUSIONS:  Investigators found non-responders may engage in electronic self-reporting, supporting the use of electronic surveys as an outbreak investigative tool. Electronic questionnaires enabled rapid survey implementation and analysis, and facilitated inter-agency collaboration. Early engagement of restaurant, distributor, and industry partners industry can lead to rapid and thorough traceback by overcoming barriers, establishing rapport, and identifying common food safety goals. In addition, pursuing multi-ingredient tracebacks early in an investigation may rule-out confounding vehicles. Early traceback initiation establishes processes and communication pathways for future traceback, may reduce time to vehicle source confirmation, and is more effectively employed with enhanced human resource capacity.  Restaurant clustering in multi-state outbreaks offers unique opportunities for hypothesis development, proactive multi-ingredient traceback, and industry collaboration.