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T5-06 Attribution of Listeria monocytogenes Human Cases to Food and Animal Sources in Northern Italy

Thursday, 30 March 2017: 11:45
314-316 (The Square)
Virginia Filipello, University of Turin, Grugliasco, Italy
Lapo Mughini-Gras, National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands
Silvia Gallina, Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d'Aosta, Turin, Italy
Ettore Amato, University of Milan, Milan, Italy
Mirella Pontello, University of Milan, Milan, Italy
Lucia Decastelli, Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d'Aosta, Turin, Italy
Marc Allard, U.S. Food and Drug Administration, College Park, MD
Eric Brown, U.S. Food and Drug Administration, College Park, MD
Sara Lomonaco, University of Turin, Grugliasco, Italy
Introduction:   Human listeriosis is a rare, but serious foodborne disease, with high hospitalization and fatality rates in at-risk population (i.e. the immunocompromised, elderly, newborns, and pregnant women). Source attribution of foodborne diseases, based on microbial subtyping, is widely used to ascertain the main sources of infection by quantifying the relative contributions of different foods to human disease.

Purpose: This study aimed to assess the contribution of different animal and food sources of human listeriosis in the Piedmont and Lombardy regions (Northern Italy) from 2005 to 2016.

Methods: A representative collection of human (n=230) and veterinary/not-human (n=440) Listeria monocytogenes isolates was selected and typed with multi-locus sequence typing (MLST) and multi-virulence locus sequence typing (MVLST). Using both MLST and MVLST data, four different source attribution modelling approaches (Asymmetric Island, STRUCTURE, Hald and Dutch models) were applied in a comparative fashion.

Results: In all models, the primary source of listeriosis cases was estimated to be dairy products (either from cattle or mixed species), accounting for up to 73% of human cases; followed by poultry (3-18%) and game meat (3-16%). Sources, like pork (2-3%) and beef (2-4%), seemed to play a minor role. Differences in attributions were observed depending on the modelling approach and typing method. Combining MLST and MVLST data did not, significantly, influence the results of attribution modeling.

Significance: Source attribution, based on microbial subtyping, is a valuable tool for quantifying the contribution of different food-animal sources of human listeriosis and to guide public health interventions. Our results provided strong evidence for dairy products as the most important source of human listeriosis in these regions and underline the lasting need for control measures aimed at reducing L. monocytogenes contamination in these products.

Back to: Technical Session 5 – Food Safety and Microbiology
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