Abstract
In May 2016, two separate clusters of febrile gastroenteritis caused by Listeria monocytogenes were detected by the local health authority in Piedmont, in northern Italy. We carried out epidemiological, microbiological and traceback investigations to identify the source. The people affected were students and staff members from two different schools in two different villages located in the Province of Turin; five of them were hospitalised. The epidemiological investigation identified a cooked beef ham served at the school canteens as the source of the food-borne outbreak. L. monocytogenes was isolated from the food, the stools of the hospitalised pupils and the environment of the factory producing the cooked beef ham. All isolates except one were serotype 1/2a, shared an indistinguishable PFGE pattern and were 100% identical by whole genome sequencing (WGS). By combining a classical epidemiological approach with both molecular subtyping and WGS techniques, we were able to identify and confirm a Listeria gastroenteritis outbreak associated with consumption of sliced cold beef ham.
Highlights
Listeria monocytogenes is a ubiquitous Gram-positive food-borne pathogen that causes listeriosis both in humans and in several animal species
When using the narrower case definition, halibut consumption again did not have a statistically significant association with the cases (RR = 1.18; 95% CI: 0.76–1.84), we considered it a chance finding and did not proceed to investigate it further
By combining an epidemiological approach and molecular typing including whole genome sequencing (WGS) techniques, we were able to identify and confirm a Listeria outbreak associated with the consumption of one food item, sliced cold beef ham
Summary
Listeria monocytogenes is a ubiquitous Gram-positive food-borne pathogen that causes listeriosis both in humans and in several animal species. Food-borne transmission of L. monocytogenes can cause a self-limited acute febrile gastroenteritis, primarily reported among healthy people. L. monocytogenes is widely distributed in natural environments and has been isolated from soil, decaying vegetation, stream water, sewage, urban environments and human and animal faeces [2]. Its ubiquity and ability to adapt and to survive under environmentally stressed conditions make it challenging to control and eradicate L. monocytogenes in foodprocessing environments and constitute a concern for the food industry [2]. The role of L. monocytogenes in food-borne outbreaks has been clearly recognised in the last decades [3,4,5,6]. Since 1993, listeriosis has been a reportable disease in Italy
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