The FDA has imposed a zero tolerance for Listeria monocytogenes in food products especially ready-to-eat items. This pathogen may be responsible for severe disease or death in the immunosuppressed and aged and is the cause of miscarriages in pregnant consumers. In recent years, listeriosis has been associated with consumption of contaminated fruit, raw milk, dairy products including soft cheeses and ice cream, cold cuts of meat, hard-cooked eggs, green produce and a range of ready-to-eat foods.
In a survey conducted in England during 2018 through 2019*, 1,050 samples of frozen fruit and vegetables were assayed for the presence of Listeria. The study was prompted by an outbreak of listeriosis involving a series of fifty-three diagnosed cases among five nations caused by contaminated frozen sweet corn packed in Hungary.
The survey revealed that one percent of fruit samples were contaminated with more than one hundred cfu/g E. coli. Two percent of fruit samples yielded Listeria monocytogenes. The study confirmed that 24 percent of frozen vegetables were contaminated with Listeria although at a level below 100 cfu/g. Listeria monocytogenes was identified in ten percent of frozen vegetables sampled The application of whole genome sequencing to 74 isolates identified genetic clusters suggesting a common source. Four were from sweet corn and one cluster each for beans, peas, peppers and broccoli.
The question arises as to whether listeriosis is a disease with a low incidence rate and high mortality as evidenced by the occurrence of infrequent cases with severe or even fatal outcomes in high-risk patients. The data from the survey suggest that listeriosis is a widespread under-diagnosed foodborne infection with low-grade morbidity and negligible mortality absent a predisposing condition. Infected individuals show mild influenza-like symptoms that do not result in medical intervention and hence diagnosis.
It would be instructive to evaluate U.S. produce and fruit consumed raw in comparison with vegetables that are cooked.
*Willis A, C. at al. Occurrence of Listeria and Escherichia coli in frozen fruit and vegetables collected from retail and catering premises in England 2018-2019. International Journal of Food Microbiology. 334;108849. December 2, 2020