Research – Listeria monocytogenes in Cooked Chicken: Detection of an Outbreak in the UK (2016-2017) and Analysis of L. monocytogenes from Unrelated Monitoring of Foods (2013-2017)


In England and Wales, Public Health England (PHE) applies whole genome sequencing (WGS) to cultures of Listeria monocytogenes recovered from human cases of listeriosis, foods and food production environments. Following the routine inspection of a small retailer in February and March 2016, two unopened packs of cooked chicken produced by the same manufacturer were contaminated with L. monocytogenes at levels of 340 and 20 CFU/g. A public recall of this product was issued in March 2016. Early in 2017, a <5 single nucleotide polymorphism (SNP) single linkage cluster was detected between the L. monocytogenes from the two cooked chicken products and cultures from five cases of human listeriosis in England and Scotland with onsets of illness between March 2016 and February 2017. Epidemiological data provided further supportive evidence that this cluster was an outbreak linked to a manufacturer of cooked chicken, who’s products were supplied to the small retailer that initiated the outbreak investigation. Unrelated to this outbreak, 34 L. monocytogenes recovered from routine food monitoring of 2,007 samples of cooked chicken during 2013 to 2017 were analysed by WGS. Previously undetected <5 SNP single linkage clusters were identified between cultures from cooked chicken and with those from two clusters and two sporadic cases of human listeriosis which were consistent with foodborne transmission. This analysis identified linkage of L. monocytogenes clusters within specific food chains more readily than traditional manual tracing. Linking of data associated with L. monocytogenes cultures from cases of listeriosis with those from unrelated food testing is a unique source of information for communicable disease risk assessment, epidemiological studies, disease prevention and control. This report provides further evidence which should act as a reminder of the association between cooked chicken consumption and human listeriosis.

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