In the United States, ready-to-eat (RTE) salads account for fewer than 5% of listeriosis cases, while deli meat accounts for over 90% of cases, according to a study that was published in the International Journal of Food Microbiology. Fernando Sampedro of the Environmental Health Sciences Division, School of Public Health at the University of Minnesota led the study titled, “Quantitative risk assessment model to investigate the public health impact of altering Listeria monocytogenes allowed levels in different food commodities.

The overall number of estimated listeriosis cases in the United States was between 1,044 and 2,089, and the chance of infection in the susceptible population such as the elderly, pregnant women, and newborns, people with underlying illness conditions was 10-10,000 higher than in the general population. The percentage of cases of listeriosis in this extremely vulnerable group ranges from 46.9% to 80.10%.

The primary goals of this study were to first conduct a retrospective evaluation of changes in Listeria monocytogenes prevalence and concentration levels in several commodities during the last 30 years. And second, to calculate the overall impact on public health of eliminating lots with particular levels of contamination from the market. RTE seafood and soft and semi-soft cheese accounted for 0.5 to 1.0% of listeriosis cases, while RTE deli meat accounting for over 90% of cases and RTE salads accounting for just under 5%. And 0.2 to 0.3% of incidents involved frozen vegetables.

The study recommends that adopting lot-by-lot testing and setting allowed quantitative regulatory limits for low-risk RTE commodities may lessen the public health impact of L. monocytogenes and increase the availability of enumeration data. In order to maximize the use of threshold values in the implementation of preventive controls for L. monocytogenes, the researchers anticipate that the study will offer assistance to national authorities as they develop effective risk management methods that take into account variations in risk levels.