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Quantitative microbiological risk assessment is intended to answer specific questions of importance to public health. For microbiological risk assessment to deliver benefits it needs to be purposefully incorporated into the decision making process. This implies a change in the way nations approach food safety and public health decisions. The novelty of microbiological risk assessment is that it quantifies the hazard throughout the food production chain and directly links this to the probability of foodborne disease. The risk assessments on L. monocytogenes and Salmonella spp. discussed in this report present powerful examples of the potential of this approach. However, it should also be realized that it would not be necessary in all cases to use such advanced tools to provide an objective basis for decisions in food safety.


The increased use of microbiological risk assessment will result in new capacity building needs. The exercise of producing these two risk assessments has been a learning experience and since it is so comprehensive it can also provide a basis for future training efforts and applied research.

An important prerequisite for microbiological risk assessment is the need for an interdisciplinary approach. There is a dual need to develop the capacity for microbiological risk assessment skills and expertise within all the relevant disciplines (microbiology, modelling, epidemiology, etc.) and to ensure that these disciplines become effectively integrated into the risk assessment process. Transparency must be maintained throughout the risk assessment process from the initial stages of building the risk assessment team, to data collection and analysis procedures. General education materials on microbiological risk assessment should be accumulated by FAO and WHO and made freely available for use by member countries.

The expert consultation suggested that the capacity for microbiological risk assessment could be strengthened through:

In this effort WHO Collaborating Centres and FAO Centres of Excellence could be involved, in conjunction with other relevant national and international entities. There is an urgent need to direct international and national support to this area. If a country does not have the resources to determine the incidence of human illness attributable to a given foodborne hazard, the use of a sentinel system through FAO and WHO would be one approach to gather the necessary information. Efforts also need to be made to collect data on the prevalence and cell numbers of microorganisms throughout the foodchain.

The consultation identified three basic approaches to meeting the microbiological risk assessment software needs of member countries. One option would be for member countries to acquire and use commercially available software. A second option would be to take the models developed for each of these risk assessments and transfer their structure and logic to a stand-alone tool. This might be done by reprogramming the mathematics and logic of the model and embedding it in a user-friendly package. The models could then be made available free of charge to member countries. A third software option would be for an international organization to develop a set of tools that would be most useful to modellers around the world and then to make them available free of charge. This approach is similar to that taken by the United States Centers for Disease Control and Prevention in the development of Epi Info. The Monte Carlo capability that is used by popular commercial software can be used, for example, to develop a set of macros that would enable users of spreadsheet software to enter data as a distribution. The software could then do Monte Carlo simulations as used in these assessments.


The expert consultation recognized these risk assessments as a resource that can be used by many parties including national authorities. Ensuring the applicability and utility of the risk assessments to all regions and all nations should be a priority for future work of national governments and FAO and WHO. This exercise in conducting risk assessment at the international level has underlined the need for data to be acquired from all regions and for the development of countries’ capacities to conduct risk assessments. The development of these capacities requires an infrastructure for the surveillance of foodborne illness and the monitoring of microbial hazards in foods throughout the foodchain and the effect of processing and other factors on the microorganism. It also requires human resources with the technical skills needed to conduct microbiological risk assessment.

7.3.1 Adaptability of the exposure assessment component

The models developed by the drafting group are applicable by others on the condition that the mathematical model is validated and the computer programs are made available. If these conditions are met, the model can be used to do risk assessment for these pathogen-commodity combinations at regional or national levels. The data used in the model must reflect the food item, raw material, manufacture, retail conditions, and consumption habits within the region under consideration. The predictive models for growth, survival or decline of microorganisms, once improved and accepted on a global basis, will still have to be used with parameters fitted to the regional or national conditions of interest.

Although some users may find value in the complete risk assessment, it is intended that any and all useful components of the assessments be exploited as fully as is possible among all member countries. While some of the concepts and data presented in these risk assessments are generic and directly adaptable, significant parts of the exposure assessment relate to specific national situations.

Although the exposure assessments are reasonably close to the exposure scenarios in some developed countries they do not truly represent any one country or situation. Therefore, the exposure assessment component should not be used without careful scrutiny of its applicability to the national situation and taking into consideration the exposure pathway in the country. Some results can be used directly as presented in the risk assessments. Some functions must be parameterized and some data must be replaced with data for a specific region or use. Other portions of the model may not be applicable at all in certain national contexts.

The two greatest concerns for adaptability of the exposure assessment are the lack of a standard format for data reporting and how to bridge data gaps. A standard format for data reporting for use in a risk assessment includes methods of collection of data and its use in a risk assessment model. In addition to the well known data collection issues of comparability and differences in methods, quality assurance etc., data collected in traditional food safety control systems are generally not collected in a manner that is well-suited to risk assessment. This would ideally require the removal of bias, accounting for confounding factors and summarizing the data in the form of a probability distribution.

FAO and WHO are in the process of developing guidelines for microbiological exposure assessment. It is anticipated that these will provide further detail on the topic of standardized reporting of data.

7.3.2 Adaptability of the hazard characterization component

The Consultation believed that the hazard characterization portions of these risk assessments offer the most readily adaptable data and models for other users of the assessment. The information there is quite generic and the approach adaptable. In those cases where the information may not be applicable it is believed that the required data can be collected. However, within any human population there are sub-groups characterized by different levels of susceptibility to infection. The degree of susceptibility and size of these sub-groups have to be defined carefully. It should be noted that collection of these data would be less likely in nations lacking a risk assessment infrastructure. The experts believed that the dose-response curves used in these risk assessments have more general applicability and that they are the best currently available for general use.

7.3.3 Other applications of the FAO/WHO risk assessment documents

The expert consultation concluded that there is a considerable amount of useful information made available through these risk assessments for those planning to undertake a quantitative microbiological risk assessment. For example, the dose-response model based on outbreak data provides meaningful estimates of the probability of illness upon ingestion of a dose of Salmonella spp. There is also information on the dose-response relationship for L monocytogenes and an estimation of relative risks for the more susceptible subpopulations.

This Salmonella spp. risk assessment provides information that would be useful in determining the impact intervention strategies may have on reducing cases of salmonellosis from contaminated eggs and poultry. In the risk assessment of Salmonella spp. in broiler chickens, for example, it was determined that there is a relationship between changing the prevalence of Salmonella spp. on the broiler chickens and reducing the risk of illness per serving. In the risk assessment of Salmonella Enteriditis in eggs, reducing the prevalence of Salmonella Enteriditis in poultry flocks was directly proportional to the reduction in risk to human health. The model can also be used to estimate the change in risk of human illness from changing storage times or temperature of eggs. The Listeria risk assessment indicates that measures that reduce the prevalence of food servings containing the highest numbers of L. monocytogenes at the point of consumption would contribute greatest to reducing disease incidence.

The reports presented to the expert consultation by the drafting group also provide an example of a format for organizing the available information in a readable way, connecting problems in food with human health outcomes. They explain clearly steps taken to gather the statistics that were used. They also provide scientific advice and analysis that may be useful for establishing regulatory policies for control of foodborne disease in different countries. For example, the Listeria report indicates that on a per serving basis foods where growth of L monocytogenes does not occur have a lower relative risk than foods that support growth. These reports can be used to provide the scientific basis for assessing or judging the proposal before the CCFH on microbiological criteria for RTE foods. In addition the risk assessments have identified important data gaps which can be used by societies to prioritise research.

[7] Regional in this case means areas with similar food production and consumption patterns and can be within a single country or cover similar areas within several countries.

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