Diarrhea — Symptoms, Causes & Treatment | MyMedicPlus

Diarrhea is defined as the passage of three or more loose or watery stools per day, or more frequently than is normal for the individual. It is classified by duration: acute diarrhea lasts under 14 days (most commonly infectious or food-related and self-limiting); persistent diarrhea lasts 14-29 days; and chronic diarrhea persists 30 days or more, indicating an underlying structural, inflammatory, or functional gastrointestinal disorder requiring investigation. Globally, diarrhea causes approximately 2 billion cases of illness and over 1.5 million deaths annually — predominantly in children under 5 in low-income countries, where it remains the second leading cause of childhood mortality after pneumonia. In high-income countries, acute diarrhea from viral gastroenteritis is extremely common but rarely life-threatening in otherwise healthy adults with access to oral rehydration therapy. The primary danger of all forms of diarrhea is dehydration and electrolyte imbalance, which can be fatal in vulnerable groups — infants, the elderly, and immunocompromised patients — without prompt fluid replacement.

Acute infectious diarrhea: viral — norovirus (most common cause in adults worldwide, highly contagious in institutions), rotavirus (leading preventable cause of child diarrhea deaths prior to vaccination), adenovirus; bacterial — Campylobacter jejuni (most common bacterial gastroenteritis in the UK — from undercooked poultry), Salmonella (eggs, poultry, reptiles), enterotoxigenic E. coli (ETEC — traveller's diarrhea), Shiga toxin-producing E. coli (STEC/O157 — undercooked beef, raw vegetables; can cause haemolytic uraemic syndrome), Clostridioides difficile (C. diff — antibiotic-associated, nosocomial). Protozoal: Giardia lamblia (small intestinal malabsorptive diarrhea from untreated water or travel), Cryptosporidium (self-limiting in immunocompetent; severe in HIV/immunosuppressed), Entamoeba histolytica (amoebiasis — tropical travel). Causes of chronic diarrhea: inflammatory bowel disease (Crohn's, ulcerative colitis — most important to exclude), irritable bowel syndrome (IBS-D — most common functional cause), coeliac disease, microscopic colitis (frequent watery diarrhea in middle-aged women), bile acid malabsorption (post-cholecystectomy, Crohn's ileitis), hyperthyroidism, pancreatic exocrine insufficiency (steatorrhoea), lactose intolerance, medications (SSRIs, metformin, PPIs, antibiotics, laxative overuse), and colorectal malignancy.

Acute infectious diarrhea: loose or watery stools (3 or more per day), abdominal cramping (often colicky, better after defaecation), nausea, vomiting, low-grade fever, and malaise — viral gastroenteritis typically resolves within 48-72 hours. Dehydration warning signs requiring urgent care: dry mouth, dark urine, reduced urine output, sunken eyes, absent tears in infants, decreased skin turgor, dizziness on standing, rapid heart rate, and altered consciousness — dehydration can progress rapidly to circulatory collapse in infants and elderly. Inflammatory (dysenteric) diarrhea: bloody diarrhea with mucus, high fever, severe abdominal pain, and tenesmus (recurrent urge to defecate) — indicates bacterial dysentery (Shigella, Campylobacter, STEC), amoebic colitis, or IBD flare. Chronic diarrhea patterns: alternating diarrhea and constipation with bloating but no systemic features suggests IBS; weight loss, nocturnal diarrhea (always pathological — indicates organic disease), and rectal bleeding suggest IBD or colorectal malignancy; pale, greasy, floating, malodorous stools (steatorrhoea) indicate malabsorption — coeliac disease or pancreatic exocrine insufficiency.

Acute diarrhea in healthy adults rarely requires testing — most cases are self-limiting. Indications for stool investigation: bloody diarrhea, severe systemic illness, immunocompromised host, symptoms beyond 7 days, recent antibiotic use (C. difficile), returning tropical traveller, and suspected outbreak. Stool investigations: stool culture and sensitivity (Salmonella, Shigella, Campylobacter); Clostridioides difficile PCR toxin assay (gold standard for C. difficile); microscopy for ova, cysts, and parasites (Giardia, Cryptosporidium, Entamoeba); faecal calprotectin (elevated in IBD and infectious enterocolitis; normal in IBS — a critical discriminating test costing approximately £30 and avoiding unnecessary colonoscopy). Blood tests for chronic diarrhea: FBC (anaemia — IBD, malignancy, coeliac), CRP/ESR (elevated in IBD), coeliac antibodies (tTG-IgA — highly sensitive and specific screening for coeliac disease), thyroid function (TFT — hyperthyroidism), electrolytes, renal function, albumin (hypoalbuminaemia from protein-losing enteropathy), and B12/folate. Colonoscopy with biopsies: indicated for suspected IBD, microscopic colitis, colorectal malignancy, or persistent undiagnosed diarrhea in adults over 45. Hydrogen breath test: diagnoses lactose intolerance and small intestinal bacterial overgrowth (SIBO).

Oral rehydration is the cornerstone of diarrhea management — preventing dehydration is more important than stopping diarrhea. Oral rehydration solution (ORS — WHO formula: glucose 13.5g, NaCl 2.6g, trisodium citrate 2.9g, KCl 1.5g per litre of clean water) is as effective as IV fluids for mild-moderate dehydration in adults and children able to drink; commercial sachets (Dioralyte, Pedialyte) are convenient alternatives. IV fluids (0.9% saline or Hartmann's) for severe dehydration, persistent vomiting, or altered consciousness. Zinc supplementation (20mg daily for 14 days in children under 5) reduces diarrhea duration, severity, and risk of recurrence over the following 2-3 months — WHO/UNICEF recommendation. Antimotility agents: loperamide (2mg initially, then 1mg after each loose stool; maximum 8 doses/day) for non-inflammatory diarrhea in adults (IBS-D, traveller's diarrhea without fever or blood); NEVER use for bloody diarrhea, high fever, suspected STEC/E. coli O157 (increases HUS risk), or C. difficile colitis. Antibiotics: indicated for Shigella (azithromycin or ciprofloxacin), Campylobacter in severe/prolonged/high-risk cases (azithromycin — fluoroquinolone resistance high), Giardia (metronidazole 400mg TDS for 5-7 days or tinidazole 2g single dose), C. difficile (oral vancomycin 125mg QDS 10 days or fidaxomicin — NOT metronidazole as first-line), and traveller's diarrhea (azithromycin 1g single dose for severe cases). Probiotics (Lactobacillus rhamnosus GG, Saccharomyces boulardii) reduce acute diarrhea duration by approximately 1 day and prevent antibiotic-associated diarrhea.

Dehydration and electrolyte disturbance: the most immediate life-threatening complication — hypokalaemia (cardiac arrhythmias, muscle weakness), hyponatraemia (seizures, cerebral oedema if excessive plain water is given), and metabolic acidosis from bicarbonate loss in stool. Globally, dehydration from diarrhea kills over 1 million children annually. Haemolytic uraemic syndrome (HUS): the most feared complication of STEC (E. coli O157:H7) — triad of microangiopathic haemolytic anaemia, thrombocytopaenia, and acute kidney injury; affects 5-15% of STEC-infected children; loperamide and antibiotics are contraindicated as they worsen HUS risk. Clostridioides difficile colitis complications: toxic megacolon (life-threatening colonic dilatation — perforation risk), colonic perforation, and life-threatening sepsis — may require emergency colectomy; recurrent C. difficile affects 20-30% of treated patients. Reactive arthritis (Reiter's syndrome): joint inflammation 1-4 weeks after Salmonella, Shigella, Campylobacter, or Yersinia gastroenteritis — more common in HLA-B27 individuals; may also cause uveitis, urethritis, and skin lesions. Malnutrition: chronic or recurrent diarrhea in children causes protein-energy malnutrition, deficiencies of iron, zinc, and vitamin A, impaired growth and cognitive development, and increased susceptibility to further infections — a vicious cycle that perpetuates childhood mortality in low-income settings.

Hand hygiene with soap and water for at least 20 seconds after toilet use and before handling food is the single most effective prevention measure — alcohol hand sanitiser is NOT effective against norovirus or C. difficile spores. Food safety: cook poultry and minced meat thoroughly (internal temperature 75°C/165°F); refrigerate perishable foods promptly; use separate boards for raw and cooked foods; avoid raw unpasteurised dairy and undercooked eggs. Safe water: use bottled or boiled water in low-income or disaster settings. Vaccination: oral rotavirus vaccine in infancy (Rotarix, RotaTeq — part of routine childhood immunisation in many countries) dramatically reduces rotavirus hospitalisation and mortality; typhoid vaccine for travel to endemic regions. C. difficile prevention: judicious antibiotic prescribing (avoid unnecessary broad-spectrum antibiotics), probiotics during antibiotic courses in high-risk patients (Lactobacillus rhamnosus GG, Saccharomyces boulardii). Breastfeeding exclusively for 6 months provides passive immunological protection and significantly reduces infant diarrhea morbidity and mortality. Zinc supplementation in under-5s in low-income settings and vitamin A supplementation reduce diarrhea incidence, severity, and associated child mortality.

Seek emergency care for signs of severe dehydration: reduced consciousness, absent urine output for 8+ hours, sunken eyes, very dry mouth, rapid weak pulse, or cold extremities. In infants and young children, dehydration from diarrhoea can progress rapidly — seek urgent care if the child is unable to drink or retain fluids, has a sunken fontanelle, or is very lethargic. See your doctor for: diarrhoea persisting more than 7 days in adults (3 days in infants), blood or mucus in stool (dysentery — may indicate E. coli O157, Campylobacter, Salmonella, C. difficile, or IBD), high fever above 39°C with diarrhoea, diarrhoea after recent antibiotic use (C. difficile — submit stool sample), travel to a high-risk country, or diarrhoea in an immunocompromised patient.