The CDC’s Morbidity and Mortality Weekly Report has published a report on a gastrointestinal illness outbreak associated with rancid tortilla chips that occurred at a correctional facility in Wyoming in October 2015. This outbreak was not reported to the public when it happened last year.
A county health department notified the Wyoming Department of Health of an outbreak on October 12, 2015. Most of those sickened got sick within one to three hours after eating lunch served at the facility cafeteria at noon on October 11. Residents and staff members reported that the tortillas chips served at the lunch “tasted and smelled like chemicals.”
A case control study was conducted by the county health department and the Wyoming Department of Health. Multivariate logistic regression analysis found that tortilla chips were the only item associated with illness. Hexanal and peroxide, markers for rancidity, were found in the tortilla chips and composite food samples from the lunch. No infectious agent was detected in either food samples or human stool samples.
A total of 16 residents and staff members at a local mixed-sex correctional facility were evaluated at the medical office after reporting stomach cramps, bloating, gas, diarrhea, and burping. Active case finding was conducted October 12 to 28, 2015, using a standardized questionnaire. A case was defined as onset of nausea, stomach cramps, diarrhea, gas, or bloating in any resident or staff member October 9 to 12, 2015. A case of severe illness was defined as occurrence of vomiting or diarrhea. A total of 55 case patients were identified for a nested case-control study.
Samples of food items served at every meal at the correctional facility were frozen and stored for an extended period of time, so investigators could get frozen samples of all of the food served at the October 11 lunch meal for testing. Gas chromatography-mass spectrometry was used to examine the food samples for possible chemical contamination.
The median age of the case patients was 30 years, with a range of 20 to 77 years. The predominant symptoms reported were nausea, gas/bloating, stomach cramps, and diarrhea, with a smaller number, about 21%, reporting vomiting. Most of the patients recovered fully with a median illness duration of 24.5 hours.
No enteric pathogens were found in stool samples, and no bacterial toxins were detected in a composite sample of food items. The peroxide value of the composite food sample that contained the chips was “markedly high”, according to lab staff members.
This outbreak describes a type of outbreak where no infectious etiology was identified, but the evidence implicated a single food item. Rancidity happens when oils and fats are degraded in a food. But since about 3 to 8 weeks had elapsed between the date of the lunch and testing, rancidity of the chips at the time of service could not be confirmed.
Outbreaks of gastrointestinal illness associated with consumption of rancid food are few. This outbreak illustrates the importance of considering noninfectious etiologies of illness as well as collecting all suspected foods, including those not suspected of contamination. And specific testing methods not routinely available at public health laboratories must be used when considering rancidity as a source of illness.