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RISK ASSESSMENT AND EPIDEMIOLOGICAL INFORMATION FOR PATHOGENIC MICROORGANISMS APPLIED TO SOIL
Citation:
Eisenberg, J. AND J L. Cicmanec*. RISK ASSESSMENT AND EPIDEMIOLOGICAL INFORMATION FOR PATHOGENIC MICROORGANISMS APPLIED TO SOIL. Presented at Sustainable Land Application Conference, Lake Buena Vista, FL, January 04 - 08, 2004.
Impact/Purpose:
To inform the public.
Description:
There is increasing interest in the development of a microbial risk assessment methodology for regulatory and operational decision making. Initial interests in microbial risk assessments focused on drinking, recreational, and reclaimed water issues. More recently risk assessments were developed for exposures to contaminated food. New areas of interest include assessing risks associated with land application of municipal wastewaters, sludges, and manure. The tools required to conduct a microbial risk assessment depend on the rationale for its undertaking. In this presentation we argue that three goals of a risk assessment are to 1) provide an understanding of the risk/disease process; 2) identify the weak links in the knowledge of the risk process; and 3) provide risk estimates. To this end we present an appropriate modeling and analytic framework that accounts for the unique properties of microbial pathogens based on the pathogen sources, pathways of exposure, and media of interest. The analytical framework provides sensitivity information that can be used to develop decision trees that are useful to regulators and managers, by allowing the identification of factors that are the most important determinants of high and low risk conditions. This same decision tree can also be a useful tool at the operational level for outlining the health benefits associated with improving different components of the biosolids treatment process, for example, to determine the pathogen attenuation required to attain a low-risk condition. An example is presented for the land application of biosolids (Colford et al. 2003, Eisenberg et al. In Press).
One particular advance in the area of microbial risk assessment is the development of health risk models that explicitly account for the different transmission pathways that can result in human infection. The inclusion of these transmission pathways provided insight into the risk process that would not be predicted by a chemical-based model. For example, our simulation results suggest that intermediate rates of shedding may result in a higher attributable risk than high rates of shedding. This is due to the fact that high rates of shedding result in high levels of pathogens in the environment, which in turn can result in pathogens circulating in the community at a high rate. Infection is spread throughout the community from person-to-person or person-to-environment-to-person. Eliminating any particular environmental pathway, therefore, will have little effect on the overall level of disease. By contrast, the chemical model would simply conclude that higher levels of shedding result in high levels of pathogens, and therefore higher levels of risk.
Risk assessment models can also provide information on data gaps and data needs. Environmental data needs include; 1) surveillance data for pathogens at various points in the environmental transport process, from a contamination site to an exposure site; 2) die-off both from natural and treatment factors; and 3) information on the functional relationship between these die-off factors and various environmental factors such as temperature and humidity. Health effects data needs include 1) dose-response relationships; 2) data on household-level transmission; and 3) data on the immune process.
Colford, J. M., Jr., D. M. Eisenberg, J. N. Eisenberg, J. Scott, and J. A. Soller. 2003. A dynamic model to assess microbial health risks associated with beneficial uses of biosolid - phase I. Water Environment Research Foundation.
Eisenberg, J. N., J. A. Soller, J. Scott, D. M. Eisenberg, and J. M. Colford, Jr. In Press. A dynamic model to assess microbial health risks associated with beneficial uses of biosolids. Risk Analysis.