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Oral Transmission of Listeria monocytogenes in Mice via Ingestion of Contaminated Food
08:38

Oral Transmission of Listeria monocytogenes in Mice via Ingestion of Contaminated Food

Published on: May 6, 2013

Outbreak of listerosis due to imported cooked ham, Switzerland 2011

H Hächler1, G Marti, P Giannini

  • 1National Centre for Enteropathogenic Bacteria and Listeria (NENT), Zurich, Switzerland.

Euro Surveillance : Bulletin Europeen Sur Les Maladies Transmissibles = European Communicable Disease Bulletin
|June 4, 2013
PubMed

Insights

A 2011 listeriosis outbreak in Switzerland was linked to contaminated cooked ham. Investigations identified the Listeria monocytogenes strain in ham, leading to a product recall and enhanced food safety alerts.

Area of Science:

  • Foodborne Illness
  • Microbiology
  • Public Health

Background:

  • An outbreak of listeriosis occurred in Switzerland between April and July 2011.
  • Nine cases were registered, with six laboratory-confirmed infections with Listeria monocytogenes.

Purpose of the Study:

  • To investigate the source and characteristics of the Listeria monocytogenes strain responsible for the outbreak.
  • To identify the food vehicle and contamination pathway.

Main Methods:

  • Laboratory confirmation of Listeria monocytogenes in clinical and food samples.
  • Molecular subtyping using pulsed-field gel electrophoresis (PFGE) to characterize the bacterial strain.
  • Traceback investigation including shopper card data analysis.

Main Results:

  • A single strain of Listeria monocytogenes, serovar 1/2a with an indistinguishable PFGE pulsotype, was identified in confirmed cases.
  • The same strain was detected in cooked ham samples, with high bacterial counts (470 and 4,800 CFU/g).
  • Traceback confirmed consumption of the contaminated ham by affected individuals.

Conclusions:

  • Contaminated cooked ham was the source of the 2011 Swiss listeriosis outbreak.
  • Contamination likely occurred during the slicing and packing process at an outsourced facility, not the primary production plant.
  • The outbreak prompted product recalls and alerts through the Rapid Alert System for Food and Feed (RASFF), highlighting the importance of supply chain oversight.

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