Detection of enterohaemorrhagic Escherichia coli in patients attending hospital in Melbourne, Australia

Aims: The objectives of this study were (i) to determine the prevalence of enterohaemorrhagic Escherichia coli (EHEC) in adults and children with diarrhoea attending hospital in Melbourne, and (ii) to evaluate diagnostic assays for the detection of EHEC. Methods: EHEC were sought in 860 faecal samples (655 from children) using direct plating, a cytotoxicity assay and an enzyme immunoassay for Shiga toxin (Stx), and PCR for virulence-associated genes of EHEC. Results: EHEC were isolated from 14 of 858 (1.6%) faecal samples (excluding repeat isolates from one patient). Isolation rates in children (1.7%) and adults (1.5%) were similar. EHEC was detected 2.5 times more frequently in samples that contained blood, but this was not statistically significant. EHEC isolates were heterogeneous in terms of serotype and virulence profile, although all produced EHEC haemolysin. Of the screening assays used, direct plating on EHEC agar, assays for Stx in MacConkey broth inoculated with faeces, and detection of the genes for Stx and EHEC haemolysin were highly sensitive and specific. Conclusions: EHEC are an infrequent cause of diarrhoea in Melbourne. EHEC can readily be isolated from faeces by screening enrichment broth cultures for Stx using PCR or enzyme immunoassay, followed by isolation of the bacteria on EHEC agar.