Micro & Immunology · patient case question
Infection with which organism most likely explains the intestinal symptoms?
Patient case: Diarrhoea after repeated antibiotic courses
Patient: Female, 56 years old
Chief complaint: “My tooth still hurts, and now I'm having diarrhoea and stomach aches every day.”
History: Several courses of antibiotics from different physicians for tooth pain. Penicillin allergy with hives. Currently taking clindamycin.
Findings: Gross decay on tooth #30 with a chronic apical abscess. Afebrile. Reports watery diarrhoea for five days.
Show answer and explanation
Correct answer: B. Clostridioides difficile
- A. Lactobacillus acidophilus is a commensal and probiotic organism. It is part of what antibiotics destroy, not a cause of colitis.
- B. CORRECT. Clindamycin is the antibiotic most classically associated with Clostridioides difficile colitis. Broad-spectrum antibiotics wipe out the protective colonic flora, allowing C. difficile spores to germinate and produce toxins A and B, which damage the mucosa and produce watery diarrhoea, cramping and, in severe cases, pseudomembranous colitis and toxic megacolon. Treatment is to stop the offending antibiotic and give oral VANCOMYCIN or FIDAXOMICIN — notably not metronidazole first-line any more.
- C. E. coli causes traveller's diarrhoea and, in the O157:H7 form, haemorrhagic colitis. It is not the antibiotic-associated organism.
- D. Salmonella is a food-borne pathogen from poultry and eggs, unrelated to antibiotic exposure.
Note: This is why the AHA removed clindamycin from its endocarditis prophylaxis recommendations. For penicillin-allergic patients, cephalexin (if the reaction was not anaphylactic), azithromycin or doxycycline are now preferred.
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