COMPARISON OF VERO CELL ASSAY AND PCR AS INDICATORS OF THE PRESENCE OF VEROCYTOTOXIGENIC ESCHERICHIA-COLI IN BOVINE AND HUMAN FECAL SAMPLES

Comparisons were made between Vero cell assay (VCA) and PCR as indicat ors for the detection of verocytotoxigenic Escherichia coli (VTEC; als o known as Shiga-like toxin-producing E. coli) and as predictors of VT EC isolation from bovine and human fecal samples. Fecal samples were c ollected as part of a survey on the prevalence of VTEC on dairy farms in southern Ontario (J.B. Wilson et al., J. Infect. Dis., 174:1021-102 7, 1996). A total of 2,655 samples were examined by VCA and PCR, 2,153 originating from cattle and 502 originating from humans. Overall, 36. 2% of the samples were positive in the VCA and 38.7% were positive by PCR. Of the VCA-positive samples screened, 41.6% yielded a VTEC isolat e. For both human and bovine samples, a significant positive associati on PCR result and VCA titer (P = 0.0001) was found. In addition, there was a significant positive association between the PCR result and VTE C isolation from VCA-positive samples for cattle (odds ratio = 9.1, P < 0.0001). For bovine samples positive in the VCA, VCA titer titer was significantly associated with the probability of obtaining a VTEC iso late. Agreement between VCA and PCR was good for both bovine and human samples (kappa = 0.69 and 0.64, respectively). The sensitivity and sp ecificity of the PCR with respect to the VCA for bovine samples were 8 2.0 and 86.5%, respectively, and those for human samples were 59.3 and 98.1%, respectively. Although correlation between VCA and PCR results was not absolute, when used in conjunction, these tests complemented one another as predictors of VTEC isolation.