Previous PageTable of ContentsNext Page


6.1 Introduction

Food will always present some minimal biological risk and it is the task of the food industry to maintain the level of risk at the minimum which is practical and technologically feasible. It should be the role of official bodies to use risk analysis to determine realistic and achievable risk levels for foodborne hazards and to base food safety policies on the practical application of the results of these analyses.

Biological agents (hazards) of concern to public health include pathogenic strains of bacteria, viruses, helminths, protozoa, algae, and certain toxic products they may produce. Of these hazards, the presence of pathogenic bacteria in foods currently presents the most significant problems internationally. The analysis of risk associated with bacterial pathogens presents unique features for risk assessment. There is a need to ensure these hazards are eliminated or reduced to an acceptable level and the CAC and its subsidiary bodies have elaborated a multitude of standards and Codes of Practice which contain procedures designed to address this issue. However, the need for a more formal approach to the process of controlling biological hazards has been recognized by Codex. In adopting the Codex text on the Hazard Analysis Critical Control Point (HACCP) system, the CAC acknowledged that the HACCP system was the most cost-effective method devised to date for controlling foodborne hazards.

HACCP is a system which identifies specific hazards and preventative measures for their control. The seven principles of HACCP, as adopted by Codex, establish the framework for developing specific HACCP plans for each food product/production line combination. When developing a specific HACCP plan, the identification of all potential hazards which are "of such a nature that their elimination or reduction to acceptable levels is essential to the production of a safe food" is required. However, the determination of which potential hazards are "essential" to control, will involve a risk-based hazard assessment. This hazard assessment will result in a list of the significant hazards which should be addressed within the HACCP plan.

6.2 Risk assessment of biological hazards

Risk assessment is the scientific evaluation of the known or potential adverse health effects resulting from human exposure to foodborne hazards. It provides an estimate of the severity and likelihood of harm resulting from exposure to a hazard. When one is considering public health risks posed by chemical or biological hazards in food, the objective of a quantitative risk assessment is to derive a mathematical statement, based on the probability of certain events, of the chance of adverse health consequences resulting from exposure to an agent capable of causing harm. Possible approaches for conducting a risk assessment for foodborne pathogens include probabalistic scenario analysis, fault tree analysis, event tree analysis and following the quantitative risk assessment paradigm proposed for chemicals.

Biological hazards may act through two general mechanisms in causing human illness. One mode of action is to produce toxins which may cause effects that range from mild symptoms of short duration to severe intoxications that can have long-term or life-threatening consequences. The second mode of action is to produce pathological responses that result from ingestion of viable organisms capable of infecting the host. Threshold levels for concern are easier to quantify in the former case. In these cases, as with certain other biological agents, a quantitative risk assessment may be possible. When considering hazards from pathogenic bacteria, however, a qualitative risk assessment may be the only feasible method currently available to derive an assessment of the severity and the likelihood of harm associated with exposure through ingestion of a food. However, both the quantitative and qualitative methods will depend on the type and quality of information developed during the risk assessment process.

While the basic steps are the same, their application will be different when conducting a qualitative assessment, as the analyst will not have the information necessary to develop a mathematical estimate of the probability and/or severity of an adverse consequence. When assessing risk for some biological agents, sufficient data may be available to conduct a quantitative analysis. However, the analyst will find that in most cases the many uncertainties associated with how and when an organism may express pathogenic potential will make a quantitative assessment impractical. Further research is required to permit more accurate and quantitative assessments in the future.

In the absence of quantitative data to develop an exposure assessment, measurement of hazard levels at particular process steps, or segments of the production chain, may provide a qualitative indication of likely risks to consumers. In this respect comparative studies on biological hazard levels and qualitative estimates of the likely effects of differences to human health can be used.

6.3 Risk assessment of bacterial hazards

The analysis of risk associated with bacterial pathogens presents unique challenges. Any method used to assess the risk of hazards from foodborne bacteria will be complicated by factors resulting from methods used to grow, process, store and prepare food for consumption. These can vary greatly depending on cultural and geographical differences. Such factors describe the scenario set for a given food and are an essential element in a risk assessment for bacterial hazards.

As already noted, in many cases sufficient data will not be available to support a quantitative assessment of risk associated with pathogenic bacteria. The following present an indication of the type of challenges that make quantitative risk assessment difficult for pathogenic bacteria associated with foods.

6.3.1 Hazard identification

Bacterial agents known to cause foodborne disease have been identified by using epidemiological and other data to link the organism and its source to illness. However, as only a limited number of outbreaks are adequately investigated, it is likely that a number of bacterial pathogens in food remain to be identified.

Limitations on hazard identification include (i) the expense and difficulty involved in outbreak investigations; (ii) the lack of reliable or complete epidemiological data; and, (iii) the inability to isolate and characterize new pathogens.

6.3.2 Hazard characterization

The purpose of this step is to provide a qualitative or quantitative estimate of the severity and duration of adverse effects due to the presence of a pathogen in food. Dose response data are useful when addressing toxigenic bacteria. However, when characterizing hazards from invasive strains of pathogenic bacteria, such information may be of little utility. For many foodborne pathogenic bacteria, dose-response data are limited or non-existent. Information on which to base dose-response estimates is difficult to obtain and may also be inaccurate for a variety of reasons, such as:

  1. host susceptibility to pathogenic bacteria is highly variable;
  2. attack rates from a specific pathogen vary widely;
  3. virulence of a pathogenic species is highly variable;
  4. pathogenicity is subject to genetic variation resultant from frequent mutation;
  5. antagonism from other bacteria in foods or the digestive system may influence pathogenicity; and,
  6. foods will modulate the ability of bacteria to infect and/or otherwise affect the host.

6.3.3 Exposure assessment

An exposure assessment will give an estimate of either the number of pathogenic bacteria or the level of bacterial toxin consumed in food. While levels of chemical agents in food may change slightly due to processing, populations of bacterial pathogens are dynamic and may increase or decrease dramatically in food matrices. Changes in populations of bacteria are affected by complex interactions of factors such as those listed below:

  1. ecology of the bacterial pathogen of concern;
  2. processing, packaging and storing of food;
  3. preparation steps, such as cooking, which may inactivate bacterial agents; and,
  4. cultural factors relating to consumers.

6.3.4 Risk characterization

Characterizing the risk associated with biological pathogens will depend on the considerations and information described in the hazard identification, hazard characterization and exposure assessment steps. A risk characterization will result in a qualitative or quantitative estimate of the potential for adverse effects from a particular bacterial agent on a specific population.

It has not yet been determined whether a quantitative risk assessment approach is possible and appropriate for characterization of risk associated with foodborne bacterial pathogens. Thus, by default, the qualitative approach to characterizing risk may be the only current alternative.

The qualitative risk assessment process depends on experience with a specific food, a knowledge of ecology of bacterial pathogens, epidemiological data, and expert judgement regarding hazards associated with the manner in which the food is produced, processed, stored, and prepared for consumption.

6.4 Risk assessment of other biological hazards

The steps in risk assessment for biological hazards other than bacteria that must be followed, for example, to provide input into HACCP plans, are identical to those described above. The variations come within the steps where the particular properties of the biological agents sometimes make the assessment more simple or more difficult in terms of developing quantitative data. The factors that complicate risk assessment for foodborne biological hazards (other than bacterial hazards) vary, but are not as great as those for bacterial hazards, as the agents typically do not increase in number when in food.

6.5 Role of the CAC in risk assessment of biological hazards

Through the CAC and its subsidiary bodies, standards, guidelines and recommendations are elaborated which are designed to address food safety issues related to biological, chemical, and physical hazards. Risk assessment is a key to developing meaningful food safety standards.

For the chemical hazards, standards are generally expressed in numerical values based on scientifically derived Acceptable Daily Intake levels. In the case of biological hazards, Codex has elaborated standards, guidelines and recommendations which describe processes and procedures, the application of which supposedly eliminates hazards or reduces them to acceptable levels. For many of the procedures, there is little quantitative data or other scientific evidence to link specific procedures with potential biological hazards, or with a specific health outcome. These linkages are necessary to enable validation of procedures and processes in standards and Codes that might come before the WTO in adjudicating disputes on food safety measures. In addition, these linkages are needed to assess or validate equivalence of alternate processes and procedures. The absence of criteria to judge equivalence is detrimental to international trade because it reduces flexibility in achieving a specified outcome.

The current procedures and processes contained in Codex standards, guidelines and recommendations do not permit a comparison of relative risk or comparative risk between food safety hazards. There is no established means of comparing chemical hazards with biological hazards, or for comparing biological hazards. This may result in the choice of alternatives which increase overall health risk associated with the food. For example, the use of super-chlorinated wash water to reduce pathogenic bacterial hazards creates a chemical hazard from chloramines. As HACCP relies on a determination of the significance of hazards, methodology needs to be available to compare risks.

Previous Page Top of Page Next Page