Respiratory diphtheria — DTM&H MCQ

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HardTropical bacterial infectionsRespiratory diphtheriaDTM&H

A 7-year-old unvaccinated child in a refugee settlement has fever, sore throat, cervical swelling and a grey pharyngeal membrane that bleeds on attempted removal. Several contacts have cough and incomplete immunisation. What is the most appropriate treatment?

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Correct answer: C — Diphtheria antitoxin plus erythromycin or penicillin

The correct answer is C, diphtheria antitoxin plus erythromycin or penicillin. The stem describes classic respiratory diphtheria (fever, sore throat, cervical lymphadenopathy, and a grey adherent pseudomembrane that bleeds on removal) in an unvaccinated child within an outbreak setting among under immunised contacts. UK guidance requires that diphtheria antitoxin be given on clinical suspicion alone, since it neutralises only free circulating exotoxin and has no effect once toxin has bound to cardiac and neural tissue, so any delay for microbiological confirmation risks irreversible myocarditis and polyneuropathy. Antibiotics (erythromycin or penicillin) are given alongside to eradicate Corynebacterium diphtheriae, stop further toxin production and reduce onward transmission to the many partially immunised contacts in the settlement. Why the other options are wrong: D. Amoxicillin alone after throat culture: antibiotics without antitoxin do not neutralise toxin already released, amoxicillin is not the recommended agent, and waiting for culture delays life-saving treatment. E. Oseltamivir and droplet advice: this is antiviral treatment for influenza and has no role in a toxin-mediated bacterial infection with a pseudomembrane. B. Ceftriaxone single dose: this regimen suits conditions such as gonorrhoea or meningococcal prophylaxis, not diphtheria, and does nothing to neutralise circulating toxin. A. Supportive care while awaiting toxigenicity testing: withholding antitoxin until toxigenicity is confirmed allows ongoing toxin binding to myocardium and nerves, turning a treatable presentation into one with fixed, often fatal complications. Key point: In suspected respiratory diphtheria, give antitoxin and antibiotics immediately on clinical grounds; never wait for laboratory or toxigenicity confirmation.

Reference: UKHSA, Immunisation against infectious disease (the Green Book), Chapter 15: Diphtheria (updated 30 May 2025), and UKHSA Public health control and management of diphtheria in England (July 2025), https://assets.publishing.service.gov.uk/media/683d87d481deb72cce2680a4/Diphtheria-green_book-chapter-15-30-05-2025.pdf