The Health Protection Agency defines acute diarrhoea as 3 or more episodes of partially formed or watery stool in a day, lasting for less than 14 days. Bacterial and viral infections account for most episodes of acute diarrhoea in adults. Viruses are the most common infectious cause in the community. Among people who consult their GP, Campylobacter species and rotavirus are the most common organisms isolated, although norovirus infections are increasing (see the Clinical Knowledge Summary on diarrhoea – adults assessment).

Gastrointestinal infection affects as many as 1 in 5 people in England each year, of whom 1 in 6 presents to a GP (Wheeler et al. 1999). According to the Health Protection Agency, most infectious diarrhoea is self-limiting: nearly half of episodes last less than 1 day. In developed countries, dehydration secondary to gastroenteritis can lead to hospital admission, but death is uncommon. Older people are at greatest risk of death (see the Clinical Knowledge Summary on gastroenteritis).

Prevention or reversal of dehydration is the priority in acute diarrhoea and gastroenteritis, particularly in frail and older people. The British national formulary (BNF) advises that antimotility drugs may be used to relieve symptoms of uncomplicated acute diarrhoea in adults; it may also be necessary to use oral rehydration salt (ORS) solution.

Faecal incontinence: the management of faecal incontinence in adults (NICE clinical guideline 49) advises that antidiarrhoeal medication should be offered to people with faecal incontinence associated with loose stools once other causes (such as excessive laxative use, dietary factors and other medication) have been excluded.

The BNF advises that antispasmodics are occasionally of value in treating abdominal cramp associated with diarrhoea but they should not be used for primary treatment. Antibacterial drugs are generally unnecessary in simple gastroenteritis because the complaint usually resolves quickly without them, and infective diarrhoeas in the UK often have a viral cause. Systemic bacterial infection does, however, need appropriate systemic treatment.