I have been doing this kind of work for over 30 years and I seldom have seen such a detailed report as this done in any outbreak. Kudos to the folks at McHenry County and others involved in the investigation. Below are the bullet points – full report can be found HERE.
We do represent several of the kids impacted and will determine next steps after a few more reads of the report.
- The most likely mode of transmission of STEC in the HHS cafeteria was through an infected food handler. At the time of the investigation a HHS food handler, that worked at both the cold sandwich station, providing garnishes (lettuce and cheese) to the sandwiches, and at the cookie station was confirmed by PCR, to have been intermittently shedding STEC, Shiga toxin 2.
- Sixteen (16) cases were identified. All cases were students or non-cafeteria staff. One food handler from the HHS cafeteria tested positive for STEC 2 (Appendix E, Table 1) but reported never experiencing symptoms.
- Among the sixteen (16) cases, fifteen (15) cases (93.8%) ate from the HHS cafeteria at sometime during the school day. Of the fifteen (15) cases, all fifteen (15) cases (93.8%) ate lunch from the cafeteria.
- Stool specimen collection from food handlers confirmed that one HHS food handler was intermittently shedding STEC Shiga toxin 2 (PCR positive) as specimen #1 was negative, specimen #2 positive, specimen #3 negative, specimen #4 positive and specimens #5 and #6 were negative.
- Sixteen (16) individuals met the case definition for the case-control study conducted by the Epidemiology and Communicable Disease Programs. A case-control study only identifies a sample of ill individuals during a specific timeframe. It does not necessarily identify all individuals who became ill but only cases and controls to collect sufficient data to statistically prove a hypothesis of the cause of illness. Therefore, the total number of ill individuals identified via this case-control study may not represent the total number of ill individuals associated with this cluster of illness.
- The HHS cafeteria is the point source(s) location for the transmission of illness in this outbreak. The epidemiological investigation identified that 15 of 16 cases (93.7% of cases) ate food from the HHS Cafeteria.
- The only food items found to be significantly associated with illness were from the cafeteria, and food items from all other sources were not found to be associated with illness. Eating a sandwich from the cold sandwich station and eating cookies from the cafeteria were found to be associated with illness. All 15 cases that ate lunch from the cafeteria ate a sandwich from the cold sandwich station and all cases with information available for lettuce ate lettuce on their sandwich.
- The outbreak of STEC at HHS was linked to a multistate outbreak by WGS. However, this does not imply that the source for the multistate outbreak, which is unidentified to date, is the same as for the outbreak at HHS. It is likely that the multistate outbreak and the outbreak at HHS share a common source by a student or staff member of HHS becoming ill with STEC after exposure to the source of the multistate outbreak at an external location. Once introduced into HHS, STEC was transmitted primarily through the HHS cafeteria.
- In this illness outbreak, the likeliest scenario is that the infected food handler failed to wash their hands correctly, or thoroughly enough, or frequently enough, which resulted in contamination of either surfaces (trays, utensils food packaging, etc.) or food items at the cold sub sandwich station and cookie station. This allowed transmission of the pathogen either through contact with contaminated surfaces and/or ready-to-eat food items which acted as fomites. Without a further cooking step after contamination, the pathogen remained viable and resulted in illness following consumption. STEC can be present for up to 16 months on surfaces without proper sanitization.