TOPICS IN MICROBIAL RISK ASSESSMENT - DYNAMIC FLOW TREE PROCESS

Microbial risk assessment is emerging as a new discipline in risk asse ssment. A systematic approach to microbial risk assessment is presente d that employs data analysis for developing parsimonious models and ac counts formally for the variability and uncertainty of model inputs us ing analysis of variance and Monte Carlo simulation. The purpose of th e paper is to raise and examine issues in conducting microbial risk as sessments. The enteric pathogen Escherichia coli O157:H7 was selected as an example for this study due to its significance to public health. The framework for our work is consistent with the risk assessment com ponents described by the National Research Council in 1983 (hazard ide ntification; exposure assessment; dose-response assessment; and risk c haracterization). Exposure assessment focuses on hamburgers, cooked a range of temperatures from rare to well done, the latter typical for f ast food restaurants. Features of the model include predictive microbi ology components that account for random stochastic growth and death o f organisms in hamburger. For dose-response modeling, Shigella data fr om human feeding studies were used as a surrogate for E. coli O157:H7. Risks were calculated using a threshold model and an alternative nont hreshold model. The 95% probability intervals for risk of illness for product cooked to a given internal temperature spanned five orders of magnitude for these models. The existence of even a small threshold ha s a dramatic impact on the estimated risk.