Risk factors and diagnosis

STEC infection should be suspected in patients with diarrhoea, especially bloody diarrhoea, with recent exposure to:

• ruminant animals (cattle, sheep, goats) or their environments
• untreated water sources, for example rivers, streams and lochs or private water supplies 
• confirmed or suspected STEC cases
• high-risk foods (undercooked meat, unpasteurised milk and products, raw vegetables)
• a known or suspected local or national outbreaks of STEC infection.

Recent travel outside the UK is also a risk factor.

While most STEC infections are sporadic, it is important to maintain a high index of suspicion, even in the absence of clear risk factors.

Microbiological testing:

• Stool culture: a stool sample should be collected, indicating the presence of bloody diarrhoea or suspected STEC, and sent to the local diagnostic laboratory for urgent processing.
• Polymerase chain reaction (PCR) testing: if the stool culture is negative and STEC clinically indicated, PCR testing can be performed locally or at the Scottish E. coli O157/STEC Reference Laboratory (SERL) to detect both E. coli O157 and non-O157 STEC.
• Rectal swab: for patients with HUS unable to provide a stool sample, a rectal swab can be sent to SERL.

Laboratory processes:

• Rapid referral: promptly refer positive isolates from local diagnostic laboratory to the SERL to confirm identity and typing.
• Result notification: the referring local diagnostic laboratory will be notified immediately of positive PCR results, followed by culture results.
• Public health notification: the local diagnostic laboratory will inform the clinical team and local public health team of positive results.

Do not delay appropriate clinical and public health management while awaiting laboratory results.¹