Microbiological risk assessment (MRA) is an emerging tool for the evaluation of the safety of food and water supplies. The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) have a central role in developing and standardizing MRA at an international level, to inform risk management at both national and international levels. Elaboration of guidelines, such as these on Hazard Characterization for Pathogens in Food and Water, are important in achieving these tasks. The guidelines are primarily intended for a multidisciplinary audience, directly involved in developing and reviewing MRA documents at an international or national level. They will also be of use to risk managers who base their decisions on the risk assessment results, and need to be aware of the underlying principles and assumptions behind these assessments.
Hazard characterizations of microbiological pathogens in food and water are considered together in this document because the two cannot be effectively managed or understood in isolation from one another, despite historical differences in approaches. Water is both an ingredient of foodstuffs and an independent vehicle for human exposure to microbiological hazards through drinking, recreational activities or contact with aerosols. Pathways for human exposure to pathogens may involve both food and water, as illustrated in recent illness outbreaks resulting from wastewater re-use in the irrigation of fruits and vegetables. Reducing the public health impact of pathogens requires an understanding of the contributions of all primary routes of exposure. The use of a common approach for the characterization of microbiological hazards in food and water will foster this understanding, assist effective risk analysis and improve the protection of public health.
Ad hoc Joint FAO/WHO Expert Meetings on Microbiological Risk Assessment (JEMRA) conduct risk assessments of foodborne microbiological hazards at the international level. Risk management responsibilities for food in international trade are generally assigned to Codex Alimentarius Committees. JEMRA aims to provide a scientific basis for the relevant risk management deliberations of the Codex Alimentarius, whose purpose is to develop food standards, guidelines and related texts aimed at protecting consumer health and ensuring food fair trade practices. The JEMRA risk assessment reports also provide risk assessment information to FAO, WHO and Codex member countries.
International guidance on water quality and human health is provided by WHO through a series of guidelines. These include Guidelines for Drinking Water Quality (GDWQ), Guidelines for the Safe Use of Wastewater and Excreta in Agriculture and Aquaculture, and Guidelines for Safe Recreational Water Environments. These guidelines are based upon critical review of the best available scientific evidence and consensus, and derived by integrating information concerning adverse health effects with information concerning the effectiveness of safeguards under both normal and stressed conditions of operation (Fewtrell and Bartram, 2001). Their outputs are generalized standards for safety management that may include guidance both for good practice and for verifications (both analytical and inspection-based). These may then be adapted to take account of social, economic and environmental factors at local or national levels. Consequently, these guidelines provide the scientific basis for risk management activities of national and local policy-makers, assist in setting standards, and provide an international point of reference for the evaluation of water safety.
Risk analysis is a process comprising: risk assessment - the scientific evaluation of known or potential adverse health effects; risk management - evaluating, selecting and implementing policy alternatives; and risk communication - exchange of information amongst all interested parties. Although functional separation between these three components is important, there is increasing recognition of the necessity for interaction between them (FAO/WHO, 2002b; WHO, 2000b).
Figure 1. Components of a microbiological risk assessment
Risk assessment for microbiological hazards in foods is defined by the Codex Alimentarius Commission (CAC) as a scientifically based process consisting of four components (Figure 1): hazard identification, exposure assessment, hazard characterization, and risk characterization.
Hazard identification is predominantly a qualitative process intended to identify microorganisms or microbial toxins of concern in food or water. It can include information on the hazard of concern as well as relevant related data, such as clinical and surveillance data.
Exposure assessment should provide an estimate, with associated uncertainty, of the occurrence and level of the pathogen in a specified portion of food at the time of consumption, or in a specified volume of water using a production-to-consumption approach. While a mean value may be used, more accurate estimates will include an estimate of the distribution of exposures. This will typically include identification of the annual food and water consumption frequencies and weights or volumes for a given population or subpopulations(s), and should combine the information to estimate the population exposure to pathogens through a certain food or water commodity.
Hazard characterization provides a description of the adverse health effects that may result from ingestion of a microorganism. When data are available, the hazard characterization should present quantitative information in terms of a dose-response relationship and the probability of adverse outcomes.
Risk characterization is the integration of the three previous steps to obtain a risk estimate (i.e. an estimate of the likelihood and severity of the adverse health effects that would occur in a given population, with associated uncertainties).
The goal of a risk assessment may be to provide an estimate of the level of illness from a pathogen in a given population, but may also be limited to evaluation of one or several step(s) in a food production or processing system. When requesting a risk assessment, the risk manager should be specific with regard to the problem with which the risk manager needs to deal, the questions to be addressed by the risk assessment, and an indication of the measures the manager would consider or has available for the reduction of illness.
This present document is intended to provide a practical framework and a structured approach for the characterization of microbiological hazards, either in the context of a full microbiological risk assessment or as a stand-alone process. It is aimed at assisting governmental and research scientists to identify the points to be addressed, the methodology for incorporating data from different sources, and the methodology of dose-response modelling.
These guidelines are not a comprehensive source of information for hazard characterization. The expertize required spans several scientific disciplines, and a multidisciplinary team is essential to the endeavour. The issues involved are complex, in particular the methodology for dose-response modelling. Rather than specifying technical details, which are evolving at a rapid pace, reference is made to additional sources of information where appropriate. Modelling decisions may require consultation with experienced statisticians, mathematicians or experts in other scientific disciplines.
These guidelines are not intended to be prescriptive, nor do they identify pre-selected, compelling options. On some issues, an approach is advocated based on a consensus view of experts (e.g. the single-hit theory, bias-neutral approach to modelling - see Section 6.3.1) to provide guidance on the current science in hazard characterization. On other issues, the available options are compared and the decision on the approach appropriate to the situation is left to the analyst. In both of these situations, transparency requires that the approach and the supporting rationale be documented in the hazard characterization.
In the case of a hazard characterization conducted as a part of a complete risk assessment of pathogens in the food chain, the documentation developed by Codex Alimentarius on MRA provides the needed context. These present guidelines are intended to complement and provide additional detail to Codex documents, which provide more general guidance on MRA (e.g. CAC, 1999)
In the case of a hazard characterization conducted as a part of a complete risk assessment of pathogens in drinking water, GDWQ and the supporting background documents provide the necessary context. In addition they provide information on the role of hazard characterization in the derivation of health-based targets for drinking-water quality.
These guidelines are limited to hazard characterization, considered either as a stand-alone process or as a component of MRA. They primarily address the effects on individual hosts of exposure to microbial pathogens. They do not consider the accumulation of individual risks over a population, nor risks of secondary transmission or the dynamic aspects thereof. These are elements of the risk characterization process.
These guidelines are limited to a consideration of the science of hazard characterization. No attempt is made to address risk management or risk communication issues, except to describe the interactions necessary to maximize the utility of the hazard characterization exercise (e.g. data collection, questions that need resolution, presentation of hazard characterization results). Issues related to establishing an appropriate level of protection are considered to be within the scope of risk management, and are not considered herein.
These guidelines are for the application of hazard characterization to microbial hazards in water and food. To date, most work has been aimed at pathogenic bacteria and viruses, and some parasitic protozoa. The principles outlined here, and in particular the descriptive methods, may also be applicable to other effects of single exposures to microorganisms or their toxins, including sequelae and chronic infections, such as by Helicobacter pylori. Effects of chronic exposure (e.g. to mycotoxins or algal toxins) may require another approach, which is more related to hazard characterization of toxic chemicals.
These guidelines focus on the adverse impact of a hazard as a result of ingestion of contaminated food and water. The adverse health effects that may occur as a result of exposure via other routes (e.g. through inhalation exposure) are not explicitly considered, but the basic principles outlined here might also be appropriate for characterizing alternative routes of exposure.