Acute diarrhoea in adults

There is no universally agreed definition for diarrhoea but the British Society of Gastroenterology defines diarrhoea as the abnormal passage of loose or liquid stools more than three times daily and/or a volume of stool greater than 200 g/day. Acute diarrhoea is usually defined as that lasting less than four weeks, and chronic diarrhoea as that lasting more than four weeks.¹

Causes of acute diarrhoea¹

• Infection (see also the separate Gastroenteritis in adults and older children and Traveller's diarrhoea articles):

  • Viral causes are often seen in primary care, including norovirus, rotavirus and sapovirus. Norovirus is the most common cause of sporadic outbreaks of gastroenteritis affecting all age groups.

  • 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, Ebola virus.

• 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 the separate Constipation in adults and Faecal incontinence articles).

• Other causes of acute diarrhoea include anxiety, food allergy, acute appendicitis, acute radiation enteritis, and intestinal ischaemia.

• Acute diarrhoea may be the early presentation of a chronic cause - for example, inflammatory bowel disease (see also the separate Chronic diarrhoea in adults article).

Epidemiology

A prospective cohort UK study reported up to 17 million cases and 1 million GP consultations attributed to acute infectious diarrhoea annually.² Severe acute diarrhoea is more common in travellers, older people, adults in contact with children, men who have sex with men and people who are immunocompromised.¹

In Africa, outbreaks of Ebola primarily occur in remote villages close to tropical rainforests in Central and West Africa. Confirmed cases of Ebola haemorrhagic fever have been reported in the Democratic Republic of the Congo (DRC, formerly Zaire), Sudan, Gabon, Uganda, Republic of Congo, Côte d'Ivoire and, for the first time, Guinea, Liberia and Sierra Leone in 2014. The 2014 Ebola outbreak was one of the largest Ebola outbreaks in history and the first in West Africa. At the time of writing, the most recent outbreak was in Uganda in 2025, caused by Sudan ebolavirus.³

Assessment¹

• Determine the frequency and severity of symptoms, including the quantity and character of the stools (for example, 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 (for example, 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 (for example, heart disease, diabetes mellitus, chronic kidney disease, immunodeficiency).

• Consider a rectal examination, particularly in people of 50 years of age or older (faecal loading in the rectum, colorectal cancer).

Investigations¹

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., E. 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 (for example, fever, dehydration), immunocompromised, recently received antibiotics or had 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 (for example, 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 - for example, 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 - for example, E. coli O157.

• Consider further investigations if it 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.

• The underlying cause may require specific treatment.⁴

• Management of complications, especially dehydration.

Drug treatment⁴

• Some people may wish to take symptomatic treatment for acute diarrhoea. Antimotility drugs relieve symptoms of acute diarrhoea. Antispasmodics are occasionally useful for treating abdominal cramp associated with diarrhoea.

• Loperamide (an antimotility drug) may be used for symptom relief of acute nonspecific watery diarrhoea, including traveller's diarrhoea.⁵ It should, however, be avoided in suspected or confirmed conditions where toxic megacolon is a potential complication (for example, C. difficile infection, ulcerative colitis), and it may cause complications in people with Shigella or Shiga-toxin producing E. coli infections. Loperamide should therefore not be used in people with bloody diarrhoea, or diarrhoea with fever.⁶

• 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 traveller's diarrhoea.

• Colestyramine provides symptomatic relief of diarrhoea following ileal disease or resection.

When to consider hospital admission or referral¹

• 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 - for example, co-existing medical conditions (immunodeficiency, inflammatory bowel disease, heart disease, diabetes mellitus, renal impairment), drug therapy (for example, immunosuppressants or systemic steroids).

• Refer if the diagnosis remains uncertain or a chronic cause is suspected, requiring further investigation.

• Refer adults using a suspected cancer pathway referral (for an appointment within two weeks) for colorectal cancer if:

  • They are aged 40 and over with unexplained weight loss and abdominal pain; or

  • They are aged 50 and over with unexplained rectal bleeding; or

  • They are aged 60 and over with iron-deficiency anaemia or changes in their bowel habit, or tests show occult blood in their faeces.

• Consider a suspected cancer pathway referral (for an appointment within two weeks) for colorectal cancer in:

  • Adults with a rectal or abdominal mass.

  • Adults aged under 50 with rectal bleeding and any of the following unexplained symptoms or findings:

    • Abdominal pain.

    • Change in bowel habit.

    • Weight loss.

    • Iron-deficiency anaemia.

Complications

• Dehydration and electrolyte imbalance.

• Reactive complications - for example, reactive arthritis.

• Spread of infection.

• Irritable bowel syndrome.

• Lactose intolerance.

• Haemolytic uraemic syndrome.

• Reduced drug absorption may have potentially serious consequences - for example, antiepileptic 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 two days and infection with Campylobacter spp. and Salmonella spp. 2-7 days.

• Giardia spp. infection may persist and cause chronic diarrhoea.

• Diarrhoea is a major cause of childhood mortality globally, although deaths in under-5s from diarrhoeal illnesses have decreased substantially over the past two decades.⁷ This is likely to be due to vaccine use (particularly rotavirus), preventative measures such as access to clean drinking water, sanitation, and hygiene measures, and better access to treatment, such as oral rehydration therapy.