Experts have made several recommendations ahead of a potential update to guidelines relating to the control of Listeria in food.

Consumer practices deviating from the intended use of a food highlights the need for improved labeling about correct preparation and businesses need to assess the potential impacts of climate change, said scientists brought together by the United Nation’s Food and Agriculture Organization (FAO) and World Health Organization (WHO).

The FAO/WHO Joint Expert Meeting on Microbiological Risk Assessment (JEMRA) met in Geneva, Switzerland, from late May to early June 2023, to perform risk assessments of Listeria monocytogenes in selected foods using models developed since a previous meeting.

In the first meeting, the expert group worked on models for lettuce, cantaloupe, frozen vegetables and ready-to-eat (RTE) fish and said they should be programmed, tested and reviewed.

During the second meeting, several risk assessment models were developed and evaluated to characterize the risk of listeriosis because of consumption of diced RTE cantaloupe, frozen vegetables, and cold-smoked RTE fish. However, the model for lettuce was not ready for evaluation.

The meetings come in response to a Codex Committee on Food Hygiene request to undertake a production-to-consumption risk assessment of Listeria monocytogenes in food. This will inform any future revision of guidelines on general principles of food hygiene to control the pathogen in food.

Main findings
Risk assessment models were considered useful and fit-for-purpose but the dose-response model could be improved by considering additional factors, such as underlying health conditions of those at risk. Experts said the models should remain available as open-source tools.

End-product sampling and microbiological testing on its own had little effect on reducing risk, even when applied to every lot but these methods can help verify the effectiveness of control measures.

In the diced RTE cantaloupe model, use of fit-for-purpose water in primary production and of an irrigation system that avoids contact between water and the edible part of the crop reduced the risk. Poor management of wash water and of environmental hygiene during processing increased risk.

Climate change could increase the prevalence of Listeria in soil, lead to a decrease in agricultural water quality and an increase in storage temperature.

Blanching reduced the risk of Listeria in frozen vegetables. However, post-blanching contamination and growth of the pathogen may occur. If non-RTE frozen vegetables are consumed without adequate cooking, then defrosting practices influence the risk.

Higher Listeria levels on incoming fish and poor environmental hygiene practices during filleting and slicing increased the risk. Addition of lactic acid and diacetate or lactic acid bacteria culture to the product lowered the risk due to reduced growth. For the climate, an increase in initial levels of Listeria in raw fish and in the storage temperature during shelf-life of the product could lead to a bigger risk.

Help on foodborne disease burden wanted
WHO has asked for experts who can contribute to developing estimates of the global burden of foodborne disease. The agency is in the process of updating 2010 estimates that were published in 2015. Revised figures should be available in 2025.

The main role would be participating in a structured expert elicitation study on the attribution of diseases to food and other pathways. A team under Dr. Tina Nane, associate professor at Delft University of Technology, was selected to lead the study through a bidding process.

The Foodborne Disease Burden Epidemiology Reference Group (FERG) is supporting WHO in the efforts. Estimating the global burden of foodborne disease involves different data from various sources.

Systematic reviews and surveillance data will provide an estimate of the true incidence of disease caused by hazards that can be transmitted by food. Then, disease models are used to estimate the impacts of these diseases on mortality and disability-adjusted life years (DALYs). Source attribution is another step in the work. The selection process started Aug. 1, 2023 and continues onward.

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