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Listeria lessons

Listeria lessons

By Roy Betts - March 2020

Over the past year Listeria appears to have re-emerged as an organism of great importance, with a number of high-profile outbreaks. Over 2018 we had the world’s largest recorded Listeria outbreak in South Africa, affecting over 1,000 people and causing at least 216 deaths. This was traced to a contaminated cooked meat product known as polony. This was followed by a Europe-wide outbreak which occurred later that year, associated with frozen sweetcorn, causing around 49 cases and eight deaths.

In the UK, in 2019, hospital patients were affected when a Listeria outbreak infected nine hospital patients and caused six deaths. This incident was linked to sandwiches from a single supplier given to the patients by the hospitals concerned. Then in the summer of 2019, reports began to emerge of a substantial Listeriosis issue in southern Spain. In mid-August the Public Health body of Andalusia notified the Spanish Ministry of Health of the outbreak - a very rapid and comprehensive investigation was carried out that traced the issue one particular brand of a ready-to-eat meatloaf product, manufactured in Seville.

The Spanish investigation was very rigorous and gave much information about the epidemiology of the outbreak and a thorough analysis of those affected. Reports state that 204 people were infected, 58% were women (31 were pregnant) and 25% of cases involved people over 65 years of age. The main symptoms were acute gastroenteritis (58% of those affected), fever (47%) and meningitis (10%). Four people presented with septicaemia. Three people died due to the infection (one was over 90 years old and two were over 70) . When authorities looked at the production site, Listeria was isolated from the production line used to manufacture the product, on oven carts used to transport the meat and on needles used to inject the meat with fat before cooking. The site environmental isolates and the isolates from infected people shared the same whole genome sequence pattern, firmly linking the site’s products to the outbreak.

The results of the Spanish outbreak confirm much of what we know about Listeria and Listeriosis. The association with pregnant individuals and the elderly point to its enhanced effects on immunocompromised individuals. The varying types of symptoms noted from gastroenteritis through to more severe septicaemia and meningitis are common in Listeria outbreaks. Finally the association, yet again, with ready-to-eat chilled foods, highlights the need for manufacturers to be constantly vigilant for the presence of Listeria in production areas, and if any is found, to trace ‘root cause’ and take every step to eliminate it quickly, whilst continuing environmental screening to show the effectiveness of the elimination action.

Campden BRI offers a full range of services to those concerned about Listeria monocytogenes including accredited testing services, shelf-life evaluation with respect to Listeria, process evaluations to assure Listeria kill, and hygiene services to recommend best practice with respect to environmental testing and cleaning procedures. If the worst happens, and Listeria is detected, our troubleshooting services can rapidly put someone on site to help find the root cause and ways to eliminate the problem.


Roy Betts
+44(0)1386 84842075
roy.betts@campdenbri.co.uk