Identifying Shiga toxin-producing Escherichia coli: results of a laboratory evaluation

Laboratory procedures for identifying Escherichia coli O157 and other Shiga toxin-producing E. coli (STEC) strains vary considerably, causing concern that these infections may be underdiagnosed. E. coli O157 may be screened for by culture on sorbitol-containing selective media; however, no selective medium is available for isolation of non-O157 STEC. Shiga toxins may be detected using enzyme immunoassay or real-time polymerase chain reaction; however, the organism is not isolated for subsequent characterization. The Centers for Disease Control and Prevention (CDC) recommends using both routine bacterial culture on sorbitol-containing medium and an assay for Shiga toxins to identify STEC. An evaluation of laboratories revealed limited compliance with these recommendations. Enhancing laboratory procedures to comply with the CDC guidelines is essential for public health surveillance.