Quantitative Microbiology 2, 141±163, 2000
# 2001 Kluwer Academic Publishers. Manufactured in The Netherlands.
Dose-Response Envelope for Escherichia coli
MARK R. POWELL*
US Department of Agriculture, Of®ce of Risk Assessment and Cost Bene®t Analysis, 1400 Independence Ave., SW,
Rm. 5248, Washington, DC 20250
US Department of Agriculture, Food Safety and Inspection Service, Ft. Collins, CO
US Department of Agriculture, Food Safety and Inspection Service, College Station, TX
US Food and Drug Administration, Center for Food Safety and Applied Nutrition, Washington, DC
US Department of Agriculture, Food Safety and Inspection Service, Washington, DC
Received May 22, 2000; Accepted September 8, 2000
Abstract. Escherichia coli O157:H7 is an emerging food and waterborne pathogen in the U.S. and internationally.
The objective of this work was to develop a dose-response model for illness by this organism that bounds the
uncertainty in the dose-response relationship. No human clinical trial data are available for E. coli O157:H7, but such
data are available for two surrogate pathogens: enteropathogenic E. coli (EPEC) and Shigella dysenteriae. E. coli
O157:H7 outbreak data provide an initial estimate of the most likely value of the dose-response relationship within
the bounds of an envelope de®ned by beta-Poisson dose-response models ®t to the EPEC and S. dysenteriae data.
The most likely value of the median effective dose for E. coli O157:H7 is estimated to be approximately 190 000
colony forming units (cfu). At a dose level of 100 cfu, the median response predicted by the model is six percent.
Key words: risk assessment, Escherichia coli O157:H7, dose-response, water and foodborne illness
Escherichia coli O157:H7 was ®rst recognized as a human pathogen in 1982 (Riley et al.,
1983). In late 1992 and early 1993, a large multi-state outbreak of E. coli O157:H7
infections in Washington and other western states was traced to undercooked hamburgers
served at multiple outlets of the same fast food chain (Bell et al., 1994). This event thrust
E. coli O157:H7 in particular, and food safety in general, onto the public agenda.
Promulgation of the Pathogen Reduction; Hazard Analysis and Critical Control Points