ITALY – The Joint FAO/WHO Expert Meeting in Microbial Risk Assessment (JEMRA)  has developed risk assessment models for Listeria monocytogenes on leafy greens, frozen vegetables, cantaloupe melon, and ready-to-eat (RTE) seafood in response to a request by the Codex Committee on Food Hygiene.

The group also provided recommendations to inform possible future revisions to the Codex Alimentarius “Guidelines on the Application of General Principles of Food Hygiene to the Control of Listeria monocytogenes in Foods.”

Updated risk assessment models will adapt the dose response from current models, which are applicable to all food commodities and account for variation in pathogen virulence and consumer susceptibility.

Whole genome sequencing (WGS) and other genomics data on L. monocytogenes may also contribute to the risk assessment. However,  the ambiguity between the phenotypic and genotypic profiles of the pathogen should be thoroughly evaluated before being used in risk assessment.

For instance, when WGS has shown that specific STs/CCs groups are overrepresented in a given commodity, the worldwide prevalence of L. monocytogenes in exposure assessment might be substituted with the specific prevalence for STs/CCs groups.

JEMRA stated that a risk assessment model should take into account primary production to consumption, be used in a modular fashion, and be flexible for reuse with other comparable food commodities, in light of current data and risk assessment methodologies.

The experts point out that the primary production (pre-harvest) module should include how the season, agrifood practices, and climate change affect the introduction of L. monocytogenes into raw materials.

Cross-contamination from primary manufacturing to consumption should also be taken into account.

The model inputs and assumptions that have the biggest impact on the model outputs should be identified using an uncertainty and sensitivity analysis, according to JEMRA. This will help uncover pertinent “what-if” scenarios and data requirements.

In “what-if” scenarios, different modules for various stages of a food chain can be utilized to assess the effects of the stages on risk.

The experts believe that more information on L. monocytogenes in the food chain from various sampling and testing programs would help to better inform risk assessment.

Risk assessment for several STs/CCs of L. monocytogenes would be possible with knowledge of the pathogen’s prevalence, pathogenicity, and dosage response.

Leafy Greens

JEMRA identified production practices for leafy greens, such as irrigation, fertilizer, and other on-farm management techniques, as having an impact on the presence of L. monocytogenes on the farm. These practices may be modeled in a primary production (pre-harvest) module.

The experts also suggested that the risk assessment model take into account the season because it affects the microbial kinetics in soil and on leaves.

Updated risk assessment models will adapt the dose response from current models, which are applicable to all food commodities and account for variation in pathogen virulence and consumer susceptibility.

JEMRA identified the following stages to be reflected in the risk assessment: growth of leafy greens (field, controlled environment, and hydroponics), harvesting, cooling, washing, sanitizing, cutting, packaging, multiple transportation steps, display at retail, and consumer practices.

Frozen vegetables

The non-RTE, blanched, and frozen veggies are covered under the model for frozen vegetables.

The model should take post-blanching contamination into account because the primary risk factors for L. monocytogenes from frozen vegetables are focused in the stages of processing to consumption.

JEMRA highlighted steps, such as cleaning, washing, blanching, freezing, packaging, retail display, and consumer habits like defrosting, cooking, and typical practices linked to non-intended usage, to be reflected in the risk assessment.

The model should also evaluate the efficacy of sample programs at the conclusion of processing, the effectiveness of blanching or other inactivation steps prior to or following packaging, and the prevention of contamination following blanching.

Finally, the risk assessment should evaluate the impact of different consumer practices related to storage and cooking, and the impact of efforts to shift consumer practices to increase compliance with safe cooking of non-RTE frozen food.


The cantaloupe risk assessment model, which takes into account primary production through consumption, was created for whole and RTE diced cantaloupe.

Growing on the field, harvesting, cooling, washing, sanitizing, dicing, display at retail, consumer habits, and various transit procedures are some of the pertinent stages that JEMRA identified.

Opportunities for cross-contamination of L. monocytogenes throughout cantaloupe production to consumption should be taken into account and include: irrigation water and soil at pre-harvest, pooling water, food contact surfaces, dicing the fruit, and market practices.

The effectiveness of on-farm preventative measures, application of pre-harvest precautions, processing effects, and consumer practices should all be evaluated as part of the risk assessment.

RTE Seafood

The model for RTE seafood takes into consideration primary production (harvest and farming) to consumption.

Hot- and cold-smoked fish and gravad fish were proposed as representative foods for the category.

According to the experts, the risk assessment needs to be adaptable in order to account for future RTE fish items like sashimi and ceviche.

Relevant stages to be represented in the risk assessment were by identified JEMRA, including: growth of fish (open sea and aquaculture), harvesting, evisceration and head cutting, filleting, different smoking steps, gravad fish steps, freezing, slicing, packaging, multiple transportation steps, retail, and consumer handling.

Cross-contamination should be incorporated in the model since RTE fish products are produced in numerous processes, often in different facilities spanning national borders.

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