(At Step 3 of the Procedure)
Risks from microbiological hazards are of immediate and serious concern to human health. Risk Assessment will be a key element in assuring that sound science is used to establish standards, guidelines and other recommendations for food safety to ensure consumer protection and facilitate international trade. The Risk Assessment process should include quantitative information to the greatest extent possible in the estimation of risk. A Microbiological Risk Assessment should be conducted using a structured approach such as that described in this document. This document will be of primary interest to governments although other organizations, companies, and other interested parties who need to prepare a Microbiological Risk Assessment will find it valuable. Although Microbiological Risk Assessment is the primary focus of this document, the method can also be applied to certain other classes of biological hazards.
The scope of this document applies to Risk Assessment of microbiological hazards in food and water.
The Committee did not discuss any definitions contained in the 1995 joint FAO/WHO Expert Consultation on the Application of Risk Analysis to Food Standards Issues Report since they are out for comment by governments. The working definitions cited here are to facilitate the understanding of certain words or phrases used in this document and should be subject to further discussion. The italicized references are for informational purposes only and will not appear in the final Codex document.
[Default - A type of assumption used in the absence of specific data, generally selected for conservative protection of public health in the current context.]
[Infection - Successful colonization of the host by a microorganism capable of causing damage to its host (modified from Saylers and Whitt, 1994).]
[Quantitative Risk Assessment - Emphasizes reliance on numerical expressions of risk and indication of the attendant uncertainties (stated in the 1995 Expert Consultation definition on Risk Analysis)].
[Qualitative Risk Assessment - A systematic approach to data which, while forming an inadequate basis for numerical risk estimations, nonetheless, when conditioned by prior expert knowledge and identification of attendant uncertainties permits risk ranking or separation into descriptive categories of risk.]
[Risk Estimate - Estimate of the likelihood, or statistical probability, that harm will occur as a result of exposure to a risk agent (Cohrssen & Covello, 1989).]
[Sensitivity analysis - A method used to examine the behavior of a model by measuring the variation in its output resulting from changes to its inputs (Cohrssen & Covello, 1989).]
[Structured approach - A framework for systematically addressing Risk Assessment.]
[Transparency - Characteristics of a process where the rationale, the logic of development, constraints, assumptions, value judgements, decisions, limitations and uncertainties of the expressed determination are fully stated, documented, and accessible for review.]
[Uncertainty analysis - A method used to estimate the uncertainty associated with model inputs, assumptions and structure/form.]
NOTE: The Codex Secretariat is to supply the agreed upon Codex Risk Analysis definitions.
These Guidelines provide and outline of the elements of a Microbiological Risk Assessment indicating the types of decisions that need to be considered at each step. In this outline the traditional steps in the Risk Assessment process developed by the 1983 NRC Committee as modified by the 1995 Joint FAO/WHO Expert Consultation have been used.
At the beginning of a Risk Assessment the specific purpose of the particular Risk Assessment being carried out should be clearly stated. The output form and possible output alternatives of the Risk Assessment should be defined. Output might, for example, take the form of an estimate of an annual occurrence of illness, or an estimate of annual rate of illness per 100,000 population, or an estimate of the rate of human illness per eating occurrence.
Hazard identification has been defined as the identification of known or potential health effects associated with a particular agent. For microbial agents, the purpose of hazard identification is to identify the microorganisms or the microbial toxins of concern with food. Hazard identification may be a qualitative process. Hazards can be identified from relevant data sources. Information on hazards can be obtained from scientific literature, from databases such as those in the food industry, and government agencies and through expert elicitations/consultations. Relevant information includes data in areas such as: clinical studies, epidemiological studies and surveillance, laboratory animal studies, investigations of the characteristics of microorganisms, the interaction between microorganisms and their environment through the food chain from primary production up to and including consumption, and studies on analogous organisms and situations.
Exposure Assessment is the qualitative or quantitative evaluation of the degree of [hazard] intake likely to occur. This may include an assessment of the extent of actual or anticipated human exposure. For microbiological agents, Exposure Assessments might be based on the potential extent of food contamination by a particular agent, and on dietary information. Exposure assessment should specify the unit of food that is of interest, i.e., a single serving portion in most/all cases of acute illness.
Factors that must be considered for Exposure Assessment include the frequency of contamination of foods by the pathogenic agent and its level in those foods over time. These factors are influenced by the characteristics of the pathogenic agent, the microbiological ecology of the food, the initial contamination of the raw material, the level of sanitation and process controls, the methods of processing, packaging, distribution and storage of the foods, as well as any preparation steps such as cooking. Another factor that must be considered in the assessment is patterns of consumption. This relates to socioeconomic and cultural backgrounds, ethnicity, seasonality, age differences (population demographics), regional differences, and consumer preferences and behavior.
Microbial pathogen levels can be dynamic and while they may be kept low, for example, by proper time/temperature controls during food processing, they can substantially increase with abuse conditions (for example, improper food storage temperatures or cross contamination from other foods). Therefore, the Exposure Assessment should describe the pathway from production to consumption. Scenarios can be constructed to predict the range of possible exposures. The scenarios might reflect effects of processing, such as hygienic design, cleaning and disinfection, as well as the time/temperature history, and food handling and consumption patterns.
Exposure Assessment estimates the level, within various levels of uncertainty, of microbiological pathogens or microbiological toxins, and the likelihood of their occurrence in foods at the time of consumption. Qualitatively foods can be categorized according to the likelihood that the foodstuff will or will not be contaminated at its source; whether or not the food can support the growth of the pathogen of concern; whether there is substantial potential for abusive handling of the food; or whether the food will be subjected to a heat process. The presence, growth, survival, or death of microorganisms, including pathogens in foods, are influenced by processing, the storage environment, including the temperature of storage, the relative humidity of the environment, and the gaseous composition of the atmosphere. Other relevant factors include pH, moisture content or water activity (aw), nutrient content, the presence of antimicrobial substances, and competing microflora. Predictive microbiology can be a useful tool in an Exposure Assessment.
The purpose of this step is to provide a qualitative or quantitative estimate of the severity and duration of adverse effects that may result from the presence of a pathogen in food.
There are several important factors that need to be considered in Hazard Characterization. These are related to both the organism, and the human host. In relation to the organism the following are important: microorganisms are replicating; the virulence of organisms can change depending on their interaction with the host and the environment; genetic material can be transferred between organisms leading to the transfer of characteristics such as antibiotic resistance; organisms can be spread through secondary and teritary transmission; the onset of clinical symptoms can be substantially delayed following exposure; organisms can persist in certain individuals leading to continued excretion of the organism and continued risk of spread of infection; low doses of some organisms can in some cases cause a severe effect; and the attributes of a food that may alter the microbial pathogenicity, e.g., high fat content of a food vehicle.
In relation to the host the following are important: genetic factors such as Human Leucocyte Antigen (HLA) type; increased susceptibility due to breakdowns of physiological barriers; individual host susceptibility characteristics such as age, poor health, concurrent infections, immune status and previous exposure history; population characteristics such as population immunity and population behavior; and persistence of the organism in the population.
A central feature of Hazard Characterization is establishing a dose-response relationship. In the absence of a known dose-response relationship, expert elicitation could be conducted to consider various factors, such as infectivity, necessary to describe Hazard Characterizations [until specific information is available]. Additionally, experts may be able to devise ranking systems so that they can be used to characterize severity and/or duration of disease.
Risk Characterization has been defined as the integration of the Hazard Identification, Hazard Characterization, and Exposure Assessment determinations previously described into qualitative or quantitative estimates of the likelihood and severity of the adverse effects which could occur in a given population, including a description of the uncertainties and variability. These estimates can be assessed by comparison with independent epidemiological data that relate hazards to disease prevalence.
Risk Characterization brings together all of the qualitative or quantitive information of the previous steps to provide a soundly based estimate of risk for a given population or subpopulation. The weight of evidence integrating quantitative and qualitative data may permit only a qualitative estimate of risk.
The degree of confidence in the final estimation of risk will depend on the variability, uncertainty, and assumptions identified in all previous steps. Uncertainty is associated with the data themselves, and with the choice of model. Data uncertainties include those that might arise in the evaluation and extrapolation of information obtained from epidemiological, microbiological, and laboratory animal studies. Uncertainties arise whenever attempts are made to use data concerning the occurrence of certain phenomena obtained under one set of conditions to make estimations or predictions about phenomena likely to occur under other sets of conditions for which data are not available. Biological variation includes the differences in virulence that exist in microbiological populations and variability in susceptibility within the human population and particular subpopulations. It is important to demonstrate the influence of the estimates and assumptions used in Risk Assessments; for quantitative Risk Assessment this can be done using sensitivity and uncertainty analyses.
The Risk Assessment should be fully and systematically documented. To ensure transparency a formal record of the Risk Assessment, including a summary, should be prepared and made available to independent parties on request so that other risk assessors can duplicate and critique the work. The formal record and summary should indicate any constraints and assumptions relative to the Risk Assessment.
EXPLANATORY END NOTES FOR THE GENERAL PRINCIPLES OF MICROBIOLOGICAL RISK ASSESSMENT
It is anticipated that these end notes will not appear in the final Codex document. They are included in this document for informational purposes only.
Microbiological Risk Assessment must be soundly based upon science.
- Microbiological Risk Assessment should be soundly based in science. However, it must be recognized that
scientific data may be limited, incomplete or conflicting. In such cases, informed judgements will need to
be made.
There should be a functional separation between Risk Assessment and Risk Management.
- This Principle was lifted from the report of the 1995 joint FAO/WHO expert consultation “An important
Principle is the functional separation of Risk Assessment from Risk Management. However, certain
interactive elements are essential for a systematic Risk Assessment process. These elements may include
ranking of hazards in the Hazard Identification step and Risk Assessment policy issues. Where Risk
Management issues may intrude in Risk Assessment, the decision-making process should be transparent.” In
some situations the risk manager will be the best qualified individual to assess the “science” of an issue. In
such circumstances, it is more important to stress not who is the assessor and who is the manager, but the
“unbiasedness” of the assessment.
Microbiological Risk Assessment should be conducted according to a structured approach that includes Hazard Identification, Hazard Characterization, Exposure Assessment, and Risk Characterization.
A Risk Assessment should clearly state the purpose of the exercise, including the form of Risk Estimate that will be the output.
A Risk Assessment should be transparent. This requires: full and systematic documentation, statement of assumptions and value judgements and rationale, and a formal record.
Understanding any limitations that influenced a Risk Assessment is essential for transparency of the process that is important in decision making. To ensure transparency a formal record on the Risk Assessment, including a summary, should be prepared and made available to independent parties on request so that other risk assessors can duplicate and critique the work. With this in mind, the final Guidelines emphasize the importance of producing formal documentation.
[Any constraints that impact on the Risk Assessment such as cost, resources or time, should be identified and their possible consequences described.]
The square brackets reflect the need for further discussion as to whether the consideration is adequately addressed in other Principles or whether the concept should stand alone as a Principle. It should be recognized that sufficient resources will not always be available and there will typically be constraints imposed on the Risk Assessment that will have an influence on the quality of the Risk Estimate. Where such resource constraints apply, it is important for transparency purposes that these constraints be described in the formal record. Where appropriate, the record should be include an evaluation of the impact of the resource constraints on the Risk Assessment.
The Risk Estimate should contain a detailed description of uncertainty and where the uncertainty arose during the Risk Assessment process.
Understanding any limitations in the data or models that influenced a Risk Estimate is essential for transparency of the decision making process.
Data should be of sufficient quality and precision that uncertainty in the Risk Estimate is minimized as far as possible.
This Principle is intended to emphasize the importance of using the best information available when conducting a Risk Assessment in order to reduce uncertainty and to increase the reliability of the Risk Estimate. It encourages the use of quantitative information to the extent possible but does not discount the value and utility of qualitative information.
Depending upon the purpose of the Risk Assessment, a Microbiological Risk Assessment should explicitly consider the dynamics of microbiological growth, survival, and death in foods and the complexity of the interaction (including sequelae) between human and agent following consumption as well as the potential for further spread.
Wherever possible, Risk Estimates should be reassessed over time by comparison with independent human health data.
A major difference between Risk Assessment for chemical agents and microbiological agents is the availability of human health data related to the results of exposure. This factor may facilitate the opportunity to compare the Risk Estimate with resulting human disease for the purpose of gauging the reliability of the estimate. This may initiate a reevaluation of the Risk Assessment.
A Microbiological Risk Assessment may need reevaluation as new relevant information becomes available.
