Two final reports on controls measures for E. coli and for Listeria in ready-to-eat food have been unveiled by FAO and WHO.

The World Health Organization (WHO) and UN Food and Agriculture Organization (FAO) published the complete reports as part of the microbiological risk assessment series.

One Joint FAO/WHO Expert Meeting on Microbiological Risk Assessment (JEMRA) in June 2020 covered Shiga toxin-producing E. coli (STEC) in meat and dairy products while the other meeting in October and November 2020 looked at Listeria monocytogenes in ready-to-eat (RTE) food.

In 2019, the Codex Alimentarius Commission approved the development of guidelines to control STEC in beef, raw milk, and cheese produced from raw milk, leafy greens, and sprouts. JEMRA was asked for scientific advice on the effectiveness of control measures against STEC during primary production and processing of raw meat, raw milk, and raw cow’s milk cheeses. Interventions were scored as high, medium, or low based on evidence in the literature.

Evidence for control measures
Farm-based practices can reduce STEC carriage, excretion, and transmission within a herd. But this can be negated at later stages of the processing chain due to mixing with other animals. Good practices include hygienic housing and bedding, low animal density, clean drinking water, biosecurity, safe and effective sanitation, and manure management. The impact of feed additives, vaccines and nutrition strategies was mixed.

There is wide variation in reported reductions when using organic acids and other chemical agents to decontaminate pre-chill carcasses. Processing measures that reduced STEC on carcasses included steam vacuuming, hot potable water, steam pasteurization, and 24-hour air chilling. Evidence supporting bacteriophage, lactic acid treatments, and irradiation is mixed. High-pressure processing, gamma irradiation, and eBeam were effective at reducing STEC in retail packs.

The efficacy of interventions during the production of raw milk and raw milk cheeses depends on the animal origin of milk, manufacturing practices, the scale of production, and microbial load.

For raw milk, interventions using bactofugation, microfiltration, bacteriophages, eBeam, and high pressure reduced bacteria levels but they all come with logistical issues. Pasteurization is very effective.

For raw milk cheeses, the cooking, acidification, and ripening steps, or a combination of these, may reduce E. coli; however, the level of decline varied by serotype and type of cheese.

Testing is complex and STEC levels are usually low in food. A sampling of beef and raw milk products helps to verify that food safety programs are working, according to the report.

Experts said producers and processors must consider their ability and logistics to use the control measure, its practicality, regulatory status, occupational health and safety issues, and cost. They added the introduction of many interventions applied in sequence as a “multiple-hurdle scheme” to reduce STEC at several points throughout the food chain would be most effective.

Listeria findings
The Listeria meeting identified gaps in the FAO/WHO risk assessment model and agreed that updating it would help inform risk analysis strategies.

The expert group recommended that leafy greens, cantaloupe, ready-to-eat (RTE) seafood, and frozen vegetables such as peas and corn were the focus of future risk assessments. They noted fresh produce has emerged as an important source of listeriosis.

Global control of Listeria monocytogenes should continue to use an approach that does not consider subgroups while allowing risk managers in some countries to use subtype information to inform their decisions.

Efforts should be focused on the management and control of Listeria by having a comprehensive food safety management system (FSMS). A key component is environmental monitoring. Regulatory agencies were advised to use a combination of finished product testing and environmental monitoring to verify proper implementation of control strategies by businesses.

Regulation should encourage aggressive environmental monitoring to eliminate sources of Listeria. Microbiological criteria such as zero tolerance can negatively impact the implementation of FSMS and the way environmental monitoring programs are employed and reported said, experts.

Public communication should focus on informing vulnerable groups about their susceptibility and about foods that have a high risk of containing Listeria.

Scientists have since developed risk assessment models for Listeria monocytogenes in certain foods. The focus was on leafy greens, frozen vegetables, cantaloupe, and RTE seafood. Models will be tested and reviewed and then made public.