BACKGROUND: With improved prevention measures, foodborne botulism is an increasingly rare but still potentially fatal illness. An average of 17 cases are reported in the United States every year. In August 2016, a case of suspected foodborne botulism was reported in an 81 year-old female with compatible symptoms, prompting an intensive investigation into potential food sources.
METHODS: The patient, patient’s family, and co-workers were interviewed to identify potential food sources and any other potentially exposed persons. Food samples were collected from the patient’s home for laboratory testing. Epidemiologists and sanitarians conducted multiple site visits to the food establishment that prepared and sold the suspected food source. Syndromic surveillance data from area hospital emergency departments was reviewed as part of additional case-finding efforts.
RESULTS: C. botulinum toxin B was isolated from a stool specimen collected from the patient. The patient did not report consuming any home-canned goods or other food products typically associated with botulism. Of the multiple food items tested from the patient’s home, one was positive for C. botulinum: beef tamales, which the case consumed approximately 12 hours before symptom onset. Prior to sale, the store-prepared tamales had been stored in sealed plastic bags and held in a food warmer below 135°F for up to 8-16 hours. Although botulism toxin was not directly detected in the tamales, C. botulinum isolated from the tamales produced toxin B. The C. botulinum isolates from the patient and the tamales were submitted for molecular analysis. No additional cases of botulism were identified.
CONCLUSIONS: Public health and healthcare providers should be aware that ready-to-eat tamales, prepared and held in conducive conditions, can be potential vehicles for foodborne botulism. Because of the difficulties in direct detection of botulism toxin in food products, molecular analysis of isolates could play an important role in definitively determining the food source of botulism outbreaks. Tamales, the suspected food vehicle, have not been reported in recent literature as a source of botulism. This investigation emphasizes the importance of proper food service management of pre-cooked foods and the importance of considering novel vehicles for foodborne botulism.