The researchers said when rancidity is suspected as the source of illness, specific food testing methods are needed that might not be readily available at state public health laboratories.
16 residents and staff members at a Wyoming mixed-sex correctional facility fell ill in October 2015.
Hexanal and peroxide, markers for rancidity, were detected in tortilla chips and composite food samples from the lunch.
Rancidity results from degradation of oils and fats, a process that can occur through exposure to heat and light, and can affect the taste and quality of food
Residents and staff members reported that tortilla chips served at the lunch tasted and smelled like chemicals but they still ate them.
No infectious agent was found in human stool specimens or food samples and testing of lunch items did not identify any unusual chemical.
In outbreaks caused by chemical contamination, people typically experience nausea, vomiting, and neurologic symptoms; case-patients in this outbreak did not report such symptoms, and only 21% reported vomiting. Instead, >70% had nausea, burping, gas or diarrhea.
Examination of samples
Frozen food samples were examined using gas chromatography–mass spectrometry to assess for possible chemical contamination or unusual added substances.
They detected hexanal, used as a measure of rancidity in the tortilla chip sample.
A private food testing laboratory tested a frozen mixture of beef and beans, nacho cheese sauce, tortilla chips, and Spanish rice (composite sample) for bacterial toxins and peroxide levels.
They measured the peroxide value, another marker for rancidity, in the composite sample of frozen lunch items and found it was 377meq/kg.
Lab staff said this value was markedly high, but they could not provide any reference ranges because of a lack of food not suspected to be contaminated but produced at the same time to serve as control samples.
Tortilla chips were purchased from a food distribution center and production and expiration dates were unknown. All remaining bags were discarded before investigators could test them.
“[Comparing] the peroxide and hexanal levels from the suspect food that was served with those of tortilla chips not suspected to be contaminated and produced by the same manufacturer on approximately the same date would have allowed investigators to better determine what levels would be expected from exposure to heat and light over time and what levels might be associated with adverse health events.
“The Wyoming correctional facility outbreak illustrates the importance of considering non-infectious etiologies of illness and collecting all suspected foods, as well as samples not suspected to be contaminated to serve as controls, to ensure that food testing can be fully interpreted.”
Source: Morbidity and Mortality Weekly Report October 28, 2016 / 65(42);1170–1173
“Gastrointestinal Illness Associated with Rancid Tortilla Chips at a Correctional Facility — Wyoming, 2015”
Authors: Tiffany Lupcho, Alexia Harrist, Clay Van Houten