Causes of acute diarrhoea^[2]

• Infection (see also separate articles Gastroenteritis in Adults and Older Children and Travellers' Diarrhoea):
  • Clostridium difficile is a common cause of infectious diarrhoea in older people who have taken antibiotics.
  • Infections that can present with bloody diarrhoea include cytomegalovirus, Campylobacter jejuni, Salmonella spp., Escherichia coli O157, Vibrio parahaemolyticus, Shigella spp., Yersinia spp., Aeromonas spp., C. difficile, Entamoeba histolytica, schistosomiasis.
• Drugs associated with diarrhoea include allopurinol, antibiotics, digoxin, colchicine, cytotoxic drugs, magnesium-containing antacids, metformin, non-steroidal anti-inflammatory drugs, proton pump inhibitors, selective serotonin reuptake inhibitors, statins, theophylline, thyroxine, and high-dose vitamin C.
• Constipation with 'overflow diarrhoea' (see also separate articles Constipation in Adults and Faecal Incontinence).
• Other causes of acute diarrhoea include anxiety, food allergy, acute appendicitis, acute radiation enteritis, intestinal ischaemia.
• Acute diarrhoea may be the early presentation of a chronic cause, eg inflammatory bowel disease (see also separate article Chronic Diarrhoea in Adults).

Epidemiology

The incidence of acute diarrhoea in the UK is about one episode per adult per year. Severe acute diarrhoea is more common in travellers, older people, adults in contact with children, homosexual men, and people who are immunocompromised.^[2]

Assessment^[2]

• Determine the frequency and severity of symptoms, including the quantity and character of the stools (eg watery, fatty, containing blood or mucus).
• Enquire about the presence of red flag symptoms:
  • Blood in the stool.
  • Recent hospital treatment or antibiotic treatment.
  • Persistent vomiting.
  • Weight loss.
  • Painless, watery, high-volume diarrhoea - increased risk of dehydration.
  • Nocturnal symptoms disturbing sleep - organic cause likely.
• Consider the underlying cause, including features suggesting infection (eg fever, recent travel abroad, contact with another person with diarrhoea, possible source of food poisoning), possible drug causes, stress or anxiety, clinical features suggesting appendicitis, recent radiotherapy, and cardiovascular risk factors (intestinal ischaemia).
• Assess for complications of diarrhoea, such as dehydration. Clinical features of dehydration:
  • Mild dehydration: lassitude, anorexia, nausea, light-headedness, postural hypotension; usually no signs.
  • Moderate dehydration: apathy, tiredness, dizziness, muscle cramps, dry tongue or sunken eyes, reduced skin elasticity, postural hypotension, tachycardia, oliguria.
  • Severe dehydration: profound apathy, weakness, confusion (leading to coma), shock, tachycardia, marked peripheral vasoconstriction, systolic blood pressure less than 90 mm Hg, oliguria or anuria.
• Consider comorbidities that may increase the risk of complications (eg heart disease, diabetes mellitus, chronic kidney disease, immunodeficiency).
• Consider a rectal examination, particularly in people 50 years of age or older (faecal loading in the rectum, colorectal cancer).

Investigations^[2]

Investigations are not always necessary for adults who present with acute diarrhoea.

• Stool specimen: pathogens routinely looked for during microbiological examination of a stool sample are Campylobacter spp., Cryptosporidium spp., Escherichia coli O157, Salmonella spp., and Shigella spp. Testing for other pathogens may be carried out depending on the clinical history.
  • Send a stool specimen for culture and sensitivity if:
    • The person is unwell (eg fever, dehydration), immunocompromised, recently received antibiotics or recent hospital admission (request specific testing for C. difficile if the patient has recently received antibiotics or has been in hospital).
    • Blood or pus in the stool.
    • The underlying cause is uncertain or the diarrhoea is persistent (eg longer than one week).
    • Diarrhoea occurs after foreign travel to anywhere other than Western Europe, North America, Australia, or New Zealand (also request tests for ova, cysts, and parasites).
  • Seek advice from the local health protection unit regarding the need for investigations if:
    • Suspected public health hazard, eg food handlers, healthcare workers, elderly residents in care homes.
    • Outbreaks of diarrhoea when isolating the organism may help pinpoint the source of the outbreak.
    • Contacts of people infected with certain organisms that may cause serious clinical sequelae, eg Escherichia coli O157.
• Consider further investigations if is suspected that there may be an underlying chronic cause.

Management

• Management is usually supportive with attention to fluid intake and nutrition. The priority when treating acute diarrhoea is the prevention or reversal of fluid and electrolyte depletion.^[3]
• The underlying cause may require specific treatment.
• Management of complications, especially dehydration.

Drug treatment^[3]

• Symptomatic treatment of acute diarrhoea may be beneficial but should only be used when there is a clear diagnosis of the underlying cause of the diarrhoea. Antimotility drugs relieve symptoms of acute diarrhoea. Antispasmodics are occasionally useful for treating abdominal cramp associated with diarrhoea.
• Antibacterial drugs are unnecessary for most cases of gastroenteritis but are required for systemic bacterial infection or for some bacterial causes of gastroenteritis such as campylobacter enteritis, shigellosis and salmonellosis. Ciprofloxacin may be useful for prophylaxis or treatment of travellers' diarrhoea.
• Colestyramine provides symptomatic relief of diarrhoea following ileal disease or resection.

Hospital admission^[2]

• Arrange emergency admission to hospital if the patient has:
  • Vomiting and inability to retain oral fluids.
  • Features of severe dehydration or shock.
• Other factors that may increase the need for admission include:
  • Older age.
  • Poor home circumstances and level of support.
  • Bloody diarrhoea.
  • Abdominal pain and tenderness (may suggest acute appendicitis or other intra-abdominal cause).
  • Increased risk of poor outcome, eg co-existing medical conditions (immunodeficiency, inflammatory bowel disease, heart disease, diabetes mellitus, renal impairment), drug therapy (eg immunosuppressants or systemic steroids).
• Refer if the diagnosis remains uncertain or a chronic cause is suspected, requiring further investigation.

Complications

• Dehydration and electrolyte imbalance.
• Reactive complications, eg reactive arthritis.
• Spread of infection.
• Irritable bowel syndrome.
• Lactose intolerance.
• Haemolytic uraemic syndrome.
• Reduced drug absorption may have potentially serious consequences, eg anti-epileptic drugs, oral contraceptives.

Prognosis

• Many people with symptoms of acute diarrhoea will improve within 2-4 days: rotavirus diarrhoea usually lasts 3-8 days, norovirus around 2 days, and infection with Campylobacter spp. and Salmonella spp. 2-7 days.
• Giardia spp. infection may persist and cause chronic diarrhoea.
• Diarrhoea is the second leading cause of death worldwide.