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Mycoplasma Pneumonia — RACP Adult Medicine MCQ

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EasyInfectious DiseasesMycoplasma PneumoniaRACP Adult Medicine

A 30-year-old man presents with atypical pneumonia: dry cough, headache, myalgia, and bilateral patchy infiltrates on CXR. He has cold agglutinins (positive bedside test with clumping of blood in EDTA tube on ice). Mycoplasma IgM is positive. What is the most likely pathogen?

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Correct answer: C — Mycoplasma pneumoniae

Atypical pneumonia (dry cough, extrapulmonary symptoms, bilateral patchy infiltrates) with cold agglutinins and positive Mycoplasma IgM is Mycoplasma pneumoniae. Cold agglutinins (IgM anti-I) occur in ~50% of cases. Treatment: doxycycline or a macrolide. Note: eTG 2025 states macrolide resistance is increasing; doxycycline is preferred. Mycoplasma can cause erythema multiforme, Stevens-Johnson syndrome, and autoimmune haemolytic anaemia.

Reference: eTG Antibiotic – 2025 – Atypical Pneumonia