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MODELING THE EFFICACY AND EFFECTIVENESS OF ESCHERICHIA COLI O157:H7 PRE-HARVEST INTERVENTIONS

Pre-harvest control of Escherichia coli O157:H7 (STEC O157) may prevent human illness by reducing the presence of STEC O157 throughout the beef production chain. Immunization of cattle with a type III secreted protein (TTSP) vaccine inhibits colonization of cattle with STEC O157 and reduces the probability for fecal shedding and hide contamination. Our objectives were to perform a meta-analysis to estimate efficacy of a three-dose regimen of TTSP vaccine at reducing the presence of STEC O157 in the feces of feedlot cattle and to test factors that might modify vaccine efficacy. Pen-level data (n=184 pens, 1,462 cattle) from four randomized controlled vaccine trials conducted from 2002-2008 at the University of Nebraska– Lincoln Agricultural Research & Development Center (Mead, NE) were analyzed. Factors explaining the probability for a positive fecal sample were tested in a generalized estimating equations (GEE) logistic regression model. An autoregressive correlation structure was defined to account for clustering of repeated test-periods within block. Clustering or potential confounding by study was accounted for by treating study as a fixed effect. Relative risk was estimated from a corresponding log-binomial GEE model. STEC O157 was detected from 661 of