Quantitative Microbial Risk Assessment
Quantitative microbial risk assessment (QMRA) is a framework and approach that brings information and data together with mathematical models to address the spread of microbial agents through environmental exposures and to characterize the nature of the adverse outcomes. While most microbes are harmless or beneficial, some are extremely dangerous – we call these Biological Agents of Concern (BAC). All BAC can cause serious and often fatal illness, but they differ greatly in their physical characteristics, movement in the environment, and process of infection. Ultimately the goal in assessing risks is to develop and implement strategies that can monitor and control the risks (or safety) and allows one to respond to emerging diseases, outbreaks and emergencies that impact the safety of water, food, air, fomites and in general our outdoor and indoor environments.
Risk by it’s nature is probabilistic and thus relies developing quantitative information.
- The definition of RISK: chance + hazard + exposure + consequence
- Risk is the likelihood of identified hazards causing harm in exposed populations in a specified time frame including the severity of the consequences.
Some other important developments of QMRA include:
- QMRA Apps and Calculators: A variety of QMRA tools begin as simplistic tools essentially established and tested Microsoft Excel spreadsheets. Some QMRA tools are being developed as standalone computer applications.
- Environmental Infection Transmission Systems (EITS): This work advances the conceptual framework for the science of environmental mediation of person to person transmitted infections by stochastic processes.
- Social Science of Risk: The risk communication is an interactive process of exchange of information and opinion on risk among risk assessors, risk managers, stakeholders and general public.
First step, state your problem
The first step in any risk assessment is to start with a question you want to answer. This can be quite broad or very narrow. Below are three examples of problems that would benefit from a risk assessment approach. We will follow these examples throughout the page so that you can get a sense of how these steps work together.
- What is the likelihood a 12 year old child will get sick with shigellosis from swimming in a contaminated lake. How should this situation be approached?
- If a crop of spinach sprayed with biosolids, how will that effect the end product being consumed in the home? Is there a risk of E. coli infection? Where in the chain can we act to reduce risk?
- If a person sick with the flu goes to work in an office building, how will they effect their coworkers. How will the virus move through the building?
|The hazard identification is both identification of the microbial agent and the spectrum of human illness and disease associated with the specific microorganism.
|The dose response analysis provides a quantitative relationship between the likelihood of adverse effects and the level of microbial exposure. Without knowing how different levels of the stressor affect the individual a sizable portion of quantified risk estimate will not be possible. The dose response assessment phase is arguably the most important phase in the QMRA paradigm.
||The exposure assessment identifies affected population, determines the exposure pathways and environmental fate and transport, calculates the amount, frequency, length of time of exposure, and estimates dose or distribution of doses for an exposure.
|The risk characterization Integrates dose-response analysis and exposure assessment to estimate the magnitude of risk, uncertainty and variability of the hazard. Assuming you find a range of values for each parameter risk characterization is the process of determining which values within these ranges to use, or how to use the ranges as a probability.
|Risk can be managed using many different strategies and is most effective when it is informed through risk characterization. The identification and evaluation of risk management strategies 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.
Haas, C.N., J.B.Rose and C.P., Gerba. 1999. Quantitative Microbial Risk Assessment.1st.Ed. John Wiley & Sons, Inc., New York.
NRC (National Research Council) 1983. Risk Assessment in the Federal Government: Managing the Process. Washington DC. National Academy Press
NRC (National Research Council) 2008. Science and Decisions: Advancing Risk Assessment. Washington DC. National Academy Press