When should I consider testing for specific pathogens in a patient with gastroenteritis?

When a patient presents with gastroenteritis, you should consider testing for specific pathogens in several circumstances, depending on their age, symptoms, and risk factors.

• For Adults:
• Consider sending a faecal specimen for routine microbiology investigation if the person is systemically unwell, needs hospital admission, or requires antibiotics ¹.
• Testing is indicated if there is blood or pus in the stool ¹.
• If the person is immunocompromised, a stool sample should be sent ¹.
• For individuals who have recently received antibiotics, a proton pump inhibitor (PPI), or been in hospital, specifically request testing for Clostridioides difficile ¹.
• If diarrhoea occurs after foreign travel, or is recurrent or prolonged, request tests for ova, cysts, and parasites, and specify the countries visited on the form ¹. This may involve sending three specimens a minimum of 2 days apart ¹.
• Consider testing if amoebae, Giardia, or cryptosporidium are suspected, particularly if diarrhoea is persistent (2 weeks or more) or the person has travelled to an at-risk area ¹.
• Testing may be needed to exclude infectious diarrhoea, for example, in cases of severe abdominal pain or exacerbation of inflammatory bowel disease ¹.
• Public Health Indications for Adults:
• Test if the patient is in a high-risk group, such as food handlers, healthcare workers, or elderly residents in care homes ¹.
• Consider testing in cases of suspected food poisoning (e.g., after a barbeque or restaurant meal, or eating eggs, chicken, or shellfish) ¹.
• Testing is important during outbreaks of diarrhoea in the family or community, as isolating the organism can help pinpoint the source ¹.
• Consider testing contacts of people infected with organisms like Escherichia coli O157 or C. difficile, or close household contacts of a person with a Giardia infection, due to potential serious clinical sequelae ¹.
• For Children (under 5s):
• Consider performing stool microbiological investigations if the child has recently been abroad ².
• Testing is also considered if the diarrhoea has not improved by day 7 ².
• If there is uncertainty about the diagnosis of gastroenteritis, microbiological investigations may be considered ².
• Perform stool microbiological investigations if you suspect septicaemia ².
• Testing is required if there is blood and/or mucus in the stool ².
• If the child is immunocompromised, stool microbiological investigations should be performed ².
• When stool microbiology is performed, ensure relevant clinical information is provided to the laboratory ².