A 19-year-old college student has 10 days of malaise, sore throat, headache, and a persistent non-productive cough. Chest examination reveals few scattered rhonchi. Total leucocyte count is normal, chest X-ray shows patchy unilateral lower-zone consolidation out of proportion to her mild signs, and indirect Coombs test is positive. Which organism is the most likely cause?
- A Streptococcus pneumoniae
- B Klebsiella pneumoniae
- C Mycoplasma pneumoniae ✓
- D Legionella pneumophila
Correct answer: C. Mycoplasma pneumoniae
Explanation
Mycoplasma pneumoniae causes walking pneumonia in young adults with a prolonged prodrome, prominent systemic symptoms, sparse physical signs disproportionate to radiographic shadowing, and haemolytic anaemia mediated by IgM cold agglutinins giving a positive Coombs test. Pneumococcal pneumonia presents abruptly with rust-coloured sputum and dense lobar consolidation, Klebsiella affects elderly alcoholics with currant jelly sputum and upper lobe cavitation, and Legionella typically causes more severe illness with hyponatraemia and gastrointestinal symptoms.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.