Experts meet to assess risk of Listeria monocytogenes in ready-to-eat food

27/01/2021 A virtual meeting of the Joint FAO/WHO Expert Meetings on Microbiological Risk Assessment (JEMRA) of Listeria monocytogenes in Ready-To-Eat (RTE) Food: Attribution, Characterization and Monitoring was held from 20 October to 6 November 2020. The purpose of the meeting was to review recent data on Listeria monocytogenes and determine the need to modify, update or develop new risk assessment models and tools for this pathogen. Prior to the meeting, a public call for data and experts was issued. In addition, background documents were prepared ahead of time for consultation by the experts. The documents included:

1. A review of  two previous JEMRA documents published in 2004: Risk assessment of Listeria monocytogenes in ready to eat foods: Interpretative summary (MRA 4) and Risk assessment of Listeria monocytogenes in ready to eat foods: Technical report (MRA5),
2. A review of current national Listeria monocytogenes surveillance and monitoring programmes,
3. A review of current microbiological/laboratory methods for Listeria monocytogenes, and
4. An update on virulence markers for Listeria monocytogenes. The meeting reviewed the summary documents and other information on outbreaks and disease attribution, virulence, population risk factors, advances in laboratory methods and surveillance. 

The risk assessment documents published in 2004 (MRA 4, MRA 5) were limited to a cross-section of RTE foods (pasteurized milk, ice cream, cold-smoked fish and fermented meats) linked to invasive listeriosis. Since the publication of those documents, outbreaks of listeriosis continue to occur across the globe associated with previously reported foods, but also with many previously unreported food vehicles, including fresh and minimally processed fruits and vegetables. The expert group concluded that future risk assessments should consider additional food vehicles and that a full farm-to-fork risk assessment be considered. While Listeria monocytogenes can infect anyone, it disproportionally affects certain highly susceptible populations. The experts recommended that future risk assessments should review groupings of susceptible groups, based on physiological risks and other socio-economic factors.  New information has emerged on Listeria monocytogenes strain variants which influences virulence and environmental tolerance. Based on a panel of specific genes, the experts suggested a potential classification system of Listeria monocytogenes strains divided into three categories of decreasing risk to human health. The expert group concluded that the development and implementation of effective surveillance systems are critical to controlling Listeria monocytogenes. The use of approved standardized laboratory methods that culture and isolate strains should be the foundation so that human, food and environmental isolates can be further characterized and inventoried.  In conclusion, the expert group identified several critical gaps in the current FAO/WHO risk assessment model and collectively agreed that updating the model would be valuable for informing risk analysis strategies, including in low and middle income countries. The experts prepared short case studies to demonstrate and highlight several key principles that should be considered in the risk assessment for Listeria monocytogenes. See an earlier news story about this meeting Listen to an interview with the meeting chairperson, Catherine Donnelly