What are the key clinical features that differentiate viral from bacterial causes of acute diarrhoea in adults?

When assessing acute diarrhoea in adults, certain clinical features can help differentiate between bacterial and viral causes, although some symptoms can overlap.

• Features more suggestive of a bacterial cause include the presence of blood or pus in the stool ¹,²,³. A high fever, particularly if severe, also suggests a bacterial infection, such as those caused by *Salmonella*, *Shigella*, or *Campylobacter*, or a cytotoxic organism like *Clostridioides difficile* ¹,². Systemic unwellness that necessitates hospital admission or antibiotic treatment is another indicator for bacterial infection ¹. Diarrhoea with an onset within 6 hours of consuming contaminated food may point to pre-formed toxins from bacteria like *Bacillus cereus* or *Staphylococcus aureus* ¹. Recent antibiotic use or hospitalisation increases the likelihood of *Clostridioides difficile* infection ¹. Specific food exposures, such as meat, shellfish, dairy, eggs, or suspected food poisoning, are often linked to bacterial causes ¹. Severe or localised abdominal pain can also suggest a bacterial infection ³.
• Features that can be present in both viral and bacterial infections include watery stools, which are associated with non-invasive and toxin-producing pathogens ¹. Vomiting is a general symptom of gastroenteritis and does not specifically differentiate between viral and bacterial causes ¹. Similarly, recent contact with someone with diarrhoea suggests an infectious cause but is not specific to the type of pathogen ¹.
• It is important to note that most cases of gastroenteritis in adults are viral and do not routinely require antibiotic treatment ². Antibiotics are generally reserved for confirmed microbial pathogens following stool culture and sensitivity testing ².