• Mode of onset (abrupt, sub-acute or gradual) and duration.
• Frequency and nature of the stools (watery or containing blood and mucus) (severe diarrhoea is defined as four or more stools daily; bloody stools are a common feature of shigellosis, salmonellosis, severe Campylobacter enteritis and ulcerative colitis, and are rare (5%) in C.difficile infection).
• Have others in the same household or who have shared the same food also developed diarrhoea?
• Other symptoms (malaise, fever, vomiting, abdominal pain)?
• Current or recent hospital inpatient (at risk of C. difficile infection)?
• Travel abroad in the past six months?
• Previous significant gastro-intestinal symptoms or known GI diagnosis?
• Medications (in particular antibiotics) taken in the six weeks before the onset of diarrhoea?
• Any other medical problems?
• HIV/AIDS or other immunosuppression? (Table 22.6)

Examination

• Severity of illness and degree of volume depletion (mental state, temperature, heart rate, blood pressure lying and sitting).
• Signs of toxic megacolon (marked abdominal distension and tenderness)? (May complicate many forms of infective colitis (including C. difficile) as well as colitis due to inflammatory bowel disease.)
• Extra-abdominal features (e.g. rash, arthropathy, uveitis)?