The QMRA Framework
The hazard identification includes both identification of the microbial agent and the description of the spectrum of human illness and disease associated with the specific microorganism. This may include for example:
- Case-Morbidity ratios, description of the symptoms and disease, case- fatality ratios, transmission routes, incubation times, impact on sensitive populations etc.
- Data from outbreaks: factors like attack rate and corrective actions.
- Microbiological information, strains, virulence factors, antibiotic resistance.
The dose response provides a quantitative relationship between infection, disease or death (or any adverse effects) and a specific dose of a microorganism which then when modelled provides the likelihood of an adverse outcome. This is from experimental data and there needs to be at least three different doses and outcomes that are less than 100% but greater than 0% in the population dosed. The results can then be modelled to produce a probability of infection, disease or mortality.
- The recommended dose-response models according to scientific criteria are included in the summary table of dose-response models.
The exposure assessment identifies the pathway(s) from the source of the pathogen to the exposure site for the affected individual or population, which addresses the transmission of the pathogen. Exposure pathways include concentrations of the pathogen, environmental fate, persistence and transport, and addresses the amount, frequency, length of time that exposure occurs, and ultimately estimates the dose or distribution of doses for the exposure event(s).
The risk characterization integrates dose-response and exposure assessment to estimate the magnitude of risk, uncertainty and variability of the probability of an adverse outcome associated with a hazard. Generally a range of values are used for each of the parameters in the dose-response and exposure assessment. Thus risk characterization examines the values within various ranges and which of the inputs (parameters) used in the risk characterization impact the outcome the most (called a sensitivity analysis).
Risk can be managed using many different strategies and is focused on reducing exposures to microbial hazards and this thus impacts the risk characterization. The identification and evaluation of risk management approaches on the basis of cost and effectiveness are integral parts of the process. In addition to quantitative evaluation, an understanding of risk perception and a plan for risk communication are also pertinent risk management activities.