Define superinfection. Describe Clostridioides difficile colitis and its management.

Definition

• Commonest with broad-spectrum agents, prolonged courses, combinations, and in the immunosuppressed, the elderly, diabetics and hospitalised patients
• The normal flora is protective — it occupies niches and competes for nutrients; removing it allows resistant organisms and fungi to flourish

Clostridioides Difficile Infection

Antibiotic disrupts the normal colonic flora → C. Difficile, already present or acquired as spores, is no longer suppressed → It multiplies and produces toxin A (enterotoxin) and toxin B (cytotoxin) → Mucosal injury and an intense inflammatory response → pseudomembranous colitis — yellowish plaques of fibrin, mucus and inflammatory cells on the colonic mucosa → Profuse watery diarrhoea, abdominal pain, fever and leucocytosis → May progress to toxic megacolon, perforation and death

• Classically caused by clindamycin, but in practice most cases follow cephalosporins, fluoroquinolones and broad-spectrum penicillins, because these are used far more often
• Proton pump inhibitors increase the risk, as does age and hospital stay
• Diagnosis — toxin detection or nucleic acid testing on stool; sigmoidoscopy shows the pseudomembranes but is rarely necessary
• Treatment — stop the offending antibiotic if possible; oral vancomycin or fidaxomicin (metronidazole is now second-line); surgery for toxic megacolon; faecal microbiota transplantation for recurrent disease, which is strikingly effective
• Antimotility drugs such as loperamide are contraindicated — they retain toxin and precipitate toxic megacolon
• Infection control — spores resist alcohol, so hand-washing with soap and water is required, not alcohol rub; and sporicidal cleaning of the environment

Prevention of Superinfection

• Use the narrowest effective antibiotic for the shortest time — the single most effective measure
• Avoid unnecessary combinations and unnecessary prophylaxis
• Review proton pump inhibitors, which are frequently continued without indication
• Attention to catheters, lines and ventilators, and their early removal
• Probiotics may reduce antibiotic-associated diarrhoea, though the evidence for preventing C. Difficile specifically is weaker

Applied Aspects

• Consider C. Difficile in any patient with diarrhoea during or within 8 weeks of antibiotic treatment, and isolate them promptly
• Oral candidiasis in an adult without an obvious cause should prompt a search for immunosuppression, diabetes, inhaled steroid use or HIV, not merely antifungal treatment
• Do not treat asymptomatic candiduria in a catheterised patient; remove or change the catheter instead
• In India, unregulated antibiotic use makes superinfection and resistant colonisation common, and a careful antibiotic history is essential in anyone presenting with diarrhoea
• The best treatment for superinfection is not another antibiotic but withdrawal of the one that caused it, wherever the primary infection allows