Question
Antibiotic associated diarrhea.
Answer
Antibiotic-associated diarrhoea: diarrhoea occurring as a consequence of antibiotic therapy, most importantly due to disruption of normal gut flora allowing overgrowth of Clostridioides difficile — the most clinically significant cause, ranging from mild self-limiting diarrhoea to severe pseudomembranous colitis.
Pathogenesis: broad-spectrum antibiotic use (classically clindamycin, fluoroquinolones, cephalosporins) disrupts the normal protective gut microbiota, allowing colonization/overgrowth of toxigenic C. difficile spores (acquired from the environment or endogenous carriage); the organism produces toxin A (enterotoxin) and toxin B (cytotoxin), which damage colonic epithelial cells, disrupt tight junctions, and trigger an intense inflammatory response, producing the characteristic pseudomembranes (composed of fibrin, inflammatory cells, and necrotic epithelium) seen on colonoscopy in severe disease.
Clinical features: watery diarrhoea (occasionally with blood/mucus), abdominal cramps, and fever, typically developing during or shortly after antibiotic exposure; severe cases can progress to toxic megacolon and colonic perforation.
Laboratory diagnosis:
- Stool toxin detection — Enzyme immunoassay (EIA) for toxin A/B, or Nucleic Acid Amplification Test (NAAT)/PCR for toxin genes (tcdA/tcdB), the current preferred, more sensitive method.
- Glutamate dehydrogenase (GDH) antigen test — a sensitive screening test (detects the organism but not specifically toxin production, so used in combination with a toxin-specific confirmatory test).
- Stool culture — on selective (cycloserine-cefoxitin-fructose) agar, technically demanding, mainly used in reference/research settings, or for further strain typing.
- Colonoscopy — visualization of characteristic pseudomembranes in more severe disease.
Management: discontinuation of the offending antibiotic where possible, and treatment with Oral Vancomycin or Fidaxomicin (metronidazole is now a less preferred alternative); infection-control precautions (contact precautions, given spore-forming, environmentally persistent transmission) are essential to prevent nosocomial spread.