Diagnosis

Diagnosis is usually made from a stool sample.

• definitive diagnosis depends on microbiological isolation and characterisation of the causative organism or the demonstration of antibodies to O157 lipopolysaccharide

Culture confirmation of E. coli O157 at the diagnostic laboratory will take 24-48 hours from receipt of the sample (local confirmation). In general, this is obtained by the following steps:

1. Examination of colonial morphology on selective media (day 1);

2. Performing a slide agglutination test on single colonies (this is usually an E. coli O157 kit- based test) (day 1);

3. Confirmation of the identity of slide agglutination positive colonies as E. coli (usually day 2).

When all 3 steps have been carried out, the isolation of E. coli O157 from the sample is `locally confirmed`.

Confirmed case: positive STEC culture or PCR shiga toxin positive result from PHE gastrointestinal bacteria reference unit (GBRU) (with or without clinical features, with or without epidemiological link to a confirmed case)

Confirmed STEC-related HUS:

• clinical features if HUS AND positive STEC culture or PCR shiga toxin positive result or serological confirmation of STEC from PHE GBRU OR
• clinical features of HUS AND diagnostic/local laboratory PCR shiga toxin positive result

Probable case:

• local O157 culture positive – diagnostic/local laboratory positive culture presumptive STEC O157 with or without clinical features, with or without epidemiological link to a confirmed case

Probable STEC-related HUS

• clinical features of HUS, with or without epidemiological link to a confirmed case, awaiting results of microbiological testing

Epidemiological link – epidemiological link to a confirmed case, awaiting results of microbiological testing OR diagnostic/local laboratory PCR shiga toxin positive, with or without clinical features of STEC

PCR probable - diagnostic/local laboratory PCR shiga toxin positive BUT negative culture for STEC O157, bloody diarrhoea/hospitalisation for acute diarrhoea, without epidemiological link to a confirmed case

Reference:

• PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections