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 humanillness 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 ofcattle 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 ofTTSP vaccine at reducing the presence of STEC O157 in the feces of feedlot cattle and to testfactors 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 estimatingequations (GEE) logistic regression model. An autoregressive correlation structure was defined to account for clustering of repeated test-periods within block. Clustering or potentialconfounding 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