Epidemiological Characterization of Listeria monocytogenes Infections in Pavia Province in 2017 Reveals the Presence of Multiple Concurrently Circulating Strains

Consumption of raw food, especially smoked fish, meat, soft cheeses, and vegetables, contaminated with Listeria monocytogenes can cause listeriosis, which can be invasive in pregnant women, elderly, and immunocompromised and diabetic patients. Through June to November of 2017, 11 patients developed invasive listeriosis in a small area of northern Italy. In the same period, 15 food samples (ready-to-eat seafood, raw vegetables, cheese samples, and salami) collected during the routine screening programs in the same area were found to be contaminated with L. monocytogenes. We characterized the isolates to determine the relatedness of L. monocytogenes strains isolated from patients and isolates from food samples and food-processing plants. Whole genome sequencing analysis showed that multiple L. monocytogenes strains were circulating in the area and no association was found between clinical and food isolates.