Acute Diarrhoea

Acute diarrhoea is the passage of 3 or more loose or watery stools in 24 hours, lasting less than 14 days. Most cases are infectious and self-limiting.

Viruses (norovirus, rotavirus, adenovirus, astrovirus, sapovirus) cause 50 to 70%. Bacteria cause 10 to 20% (Campylobacter, Salmonella, Shigella, Escherichia coli including Shiga toxin producing strains, Vibrio cholerae, Clostridioides difficile, Yersinia, Staphylococcus aureus and Bacillus cereus toxins). Protozoa (Giardia, Cryptosporidium, Entamoeba histolytica) cause a smaller proportion.

• Non-infectious causes: medicines (antibiotics, laxatives, magnesium antacids, metformin, colchicine, NSAIDs, proton pump inhibitors, chemotherapy, antihypertensives), food intolerance (lactose, fructose, artificial sweeteners), toxins (mushrooms, heavy metals, seafood toxins), acute inflammatory bowel disease, ischaemic colitis, and acute appendicitis or diverticulitis with diarrhoea.
• Epidemiology: in children under 5 years, diarrhoea is a leading cause of death worldwide, especially in low income settings. Adults average 0.5 to 1 episode a year in high income countries.
• Mechanisms: secretory diarrhoea (toxins: cholera, enterotoxigenic E. coli, large volume, watery, persisting with fasting).
• Inflammatory or invasive diarrhoea (Shigella, Campylobacter, Salmonella, enteroinvasive E. coli, with fever, blood and mucus, and faecal leucocytes).
• Osmotic diarrhoea (viral enteritis, with loss of brush border enzymes).
• Transmission is faecal oral, via contaminated food (undercooked meat, poultry, eggs, shellfish, unpasteurised milk), water, person-to-person contact, and animals (reptiles, farm animals, pets). Outbreaks occur in households, schools, nurseries, care homes and cruise ships.
• Complications: dehydration (the main cause of morbidity and death), electrolyte disturbance (hypokalaemia, hyponatraemia, hypernatraemia), acute kidney injury, bacteraemia, reactive arthritis, Guillain-Barre syndrome, haemolytic uraemic syndrome, post-infectious irritable bowel syndrome, and secondary lactose intolerance.

• Loose or watery stools with urgency, abdominal cramps, nausea, vomiting, and low grade fever. Viral gastroenteritis shows vomiting and watery diarrhoea for 1 to 3 days (norovirus) or up to 8 days (rotavirus). Bacterial infections often have fever, abdominal pain and blood or mucus (dysentery).
• Assess hydration:
  • Mild: thirst, slightly dry mouth, normal vital signs, and normal urine output (loss of 3 to 5% of body weight).
  • Moderate: marked thirst, dry mucosa, reduced skin turgor, sunken eyes, tachycardia, postural hypotension, and reduced urine output (5 to 10% loss).
  • Severe: lethargy or confusion, cold extremities, weak rapid pulse, low blood pressure, and little or no urine (above 10% loss).
  • In infants and children: irritability, sunken fontanelle, absent tears, prolonged capillary refill above 2 seconds, and fast deep breathing (acidosis).
• Differential diagnosis: appendicitis, diverticulitis, bowel obstruction, ischaemic colitis, inflammatory bowel disease, medicine effects, urinary tract infection (children), pneumonia (children), meningitis, sepsis, food allergy, coeliac disease, hyperthyroidism, malaria (fever after travel), and diabetic ketoacidosis (vomiting with abdominal pain).
• Red flags: blood in the stool, severe or constant abdominal pain, abdominal distension, persistent vomiting, signs of moderate to severe dehydration, high fever (above 39 C), age above 70 years or under 1 year, immunosuppression.
• Further red flags: diarrhoea lasting more than 7 days, recent antibiotic use or hospitalisation, recent travel, a symptomatic contact with severe illness, neurological symptoms (botulism, Guillain-Barre syndrome), pregnancy, and significant comorbidity.

• Clinical, based on the history (onset, frequency, volume, blood, vomiting, fever, exposures, contacts, travel, medicines, antibiotics, occupation), the degree of dehydration, and examination of the abdomen. Most patients need no tests.
• Perform stool culture and a polymerase chain reaction panel for: bloody diarrhoea, fever above 38.5 C, severe illness, immunosuppression, diarrhoea lasting more than 7 days, outbreak or food handler, and recent hospital contact or antibiotics (Clostridioides difficile toxin testing).
• Blood tests (full blood count, urea, creatinine, electrolytes, glucose, C-reactive protein, lactate, and blood cultures) when there is moderate to severe dehydration, sepsis, comorbidity, or older age. Check for hypokalaemia, hyponatraemia and acute kidney injury. Check the blood film for fragmented red cells and thrombocytopenia after bloody diarrhoea (haemolytic uraemic syndrome).
• Abdominal imaging for severe pain, peritonism, distension or suspected obstruction, perforation or appendicitis.
• Test persistent diarrhoea (beyond 7 to 14 days) for Giardia and Cryptosporidium antigen, ova and parasites, and Clostridioides difficile.

• Rehydration is the most important treatment:
  • Mild to moderate dehydration: low osmolarity oral rehydration solution (sodium 75 mmol/L, glucose 75 mmol/L, osmolarity about 245 mOsm/L). Give 50 mL/kg over 3 to 4 hours for mild dehydration, 100 mL/kg over 3 to 4 hours for moderate dehydration, then 10 mL/kg (children) or 200 mL (adults) for each loose stool.
  • Give small, frequent sips, or by spoon or syringe. Nasogastric administration for those who cannot drink.
  • Severe dehydration, shock, or failure of oral rehydration: intravenous Ringer lactate (or 0.9% sodium chloride) 20 mL/kg as a bolus (adults 500 to 1000 mL over 15 to 30 minutes) until the pulse and perfusion improve.
  • Then give 100 mL/kg over 3 to 6 hours, with potassium replacement (20 to 40 mmol per litre) when the patient is passing urine. Monitor electrolytes.
  • Continue breastfeeding in infants, and resume the normal diet early (within 4 hours of rehydration). Avoid sugary drinks, undiluted fruit juice and caffeine, which worsen osmotic diarrhoea.
• Zinc supplementation in children aged 6 months to 5 years: zinc sulphate or acetate 20 mg orally once daily for 10 to 14 days (10 mg daily in infants under 6 months). It shortens illness and reduces recurrence in low income settings.
• Anti-secretory and antimotility agents:
  • Racecadotril 100 mg orally 8 hourly in adults (child 1.5 mg/kg 8 hourly) until recovery, for up to 7 days, as an adjunct to rehydration.
  • Loperamide 4 mg orally at first, then 2 mg after each loose stool (maximum 16 mg per day) for up to 48 hours in adults with non-bloody, afebrile diarrhoea.
  • Avoid loperamide in children under 12 years, bloody diarrhoea, fever, suspected pseudomembranous colitis, and toxic megacolon.
  • Ondansetron 4 to 8 mg orally, sublingually or IV 8 hourly (child 0.1 to 0.15 mg/kg per dose, maximum 8 mg) for vomiting that prevents oral rehydration. Check the QT interval in those on other QT-prolonging drugs.
  • Probiotics (Lactobacillus rhamnosus GG, Saccharomyces boulardii) may reduce the duration by about 1 day in children and adults with infectious diarrhoea. Avoid in immunosuppression and critical illness.
  • Paracetamol 1 g orally 6 hourly (child 15 mg/kg every 4 to 6 hours) for fever and pain. Avoid NSAIDs in dehydration.
• Antibiotics are not needed for most acute diarrhoea, which is viral or self-limiting. Use them for specific indications:
  • Shigellosis or severe dysentery: ciprofloxacin 500 mg orally 12 hourly for 3 days (child 15 mg/kg 12 hourly), or azithromycin 500 mg orally once daily for 3 days (child 10 mg/kg once daily), or ceftriaxone 1 to 2 g IV once daily when resistance is likely.
  • Campylobacter (severe, persistent or in the immunosuppressed): azithromycin 500 mg orally once daily for 3 days. Resistance to fluoroquinolones is high.
  • Non-typhoidal Salmonella: no antibiotic for mild disease.
  • Treat non-typhoidal Salmonella when there is severe illness, bacteraemia, age above 50 years with vascular disease, age under 3 months, immunosuppression, haemoglobinopathy or prosthetic material. Use ciprofloxacin 500 mg orally 12 hourly for 5 to 7 days (or ceftriaxone 2 g IV once daily for 7 to 14 days).
  • Cholera: doxycycline 300 mg orally once (or azithromycin 1 g once, child 20 mg/kg), with intensive rehydration.
  • Shiga toxin producing E. coli (bloody diarrhoea, often without fever): avoid antibiotics and antimotility drugs, because of the risk of haemolytic uraemic syndrome. Monitor renal function and haemoglobin.
  • Clostridioides difficile: fidaxomicin 200 mg orally 12 hourly for 10 days, or vancomycin 125 mg orally 6 hourly for 10 days.
  • Giardiasis: tinidazole 2 g orally once, or metronidazole 400 mg orally 8 hourly for 5 days.
  • Amoebiasis: metronidazole 800 mg orally 8 hourly for 5 to 10 days, followed by paromomycin 25 to 35 mg/kg per day in 3 divided doses for 7 days.
• Infection control: hand washing with soap and water for 20 seconds after toilet use and before food preparation, and separate toilets where possible.
• Exclude from work, school and nursery until 48 hours after the last loose stool (longer for high risk groups and certain pathogens such as Shigella, Shiga toxin producing E. coli, typhoid and hepatitis A).
• Use chlorine based disinfection of soiled surfaces. Report notifiable infections.
• Prevention: safe water, food hygiene, hand hygiene, breastfeeding, and vaccines (rotavirus vaccine in infants, oral cholera vaccine, and typhoid vaccine for travel).
• Special groups:
  • Children: rehydration first, zinc (6 months to 5 years), feeding as soon as possible, and avoid antimotility drugs. Admit for severe dehydration, shock, persistent vomiting, bloody stool with fever, infants under 3 months, or inadequate oral intake. Weigh the child and calculate fluid deficit.
  • Pregnancy: oral rehydration, and cautious use of antibiotics (azithromycin, amoxicillin). Avoid fluoroquinolones and metronidazole in the first trimester where possible. Listeria infection is a concern with fever, so check blood cultures.
  • Elderly: higher risk of dehydration and renal impairment, so admit earlier, use intravenous fluids, and check electrolytes.
  • In the elderly, review diuretics, ACE inhibitors, angiotensin receptor blockers, NSAIDs, metformin and SGLT2 inhibitors (hold during dehydration).
  • Immunosuppressed: culture, early antibiotics, and specialist input.
  • Renal impairment: adjust doses of antibiotics and avoid NSAIDs. Hold nephrotoxic drugs during dehydration.
  • Diabetes: monitor glucose, hold metformin and SGLT2 inhibitors during dehydration, and adjust insulin.
• Follow up: review in 48 hours if symptoms are not improving, and sooner for red flags. Refer to hospital for severe dehydration, sepsis, haemolytic uraemic syndrome, persistent bloody diarrhoea, or inability to maintain oral intake. Refer to gastroenterology if diarrhoea lasts more than 14 days.