USMLE PRACTICE QUESTION OF THE WEEK
Question for November 14, 2025
A 25-year-old previously healthy man presents with 6 days of fever, dry cough, malaise, and headache. Several teammates on his recreational soccer team have similar symptoms. He denies dyspnea or chest pain. Temperature is 38.2°C (100.8°F), pulse 96/min, blood pressure 118/68 mm Hg, oxygen saturation 97% on room air. Lung exam reveals scattered expiratory crackles; no focal egophony is noted. Chest radiograph shows patchy bilateral interstitial infiltrates without lobar consolidation or pleural effusion.
Which of the following pathogens is the most likely cause?
Which of the following pathogens is the most likely cause?
Correct Answer:
B. Mycoplasma pneumoniae
Correct Answer Explanation:
Young adults with subacute “walking” pneumonia, low-grade fever, headache, dry cough, and diffuse interstitial infiltrates most likely have Mycoplasma pneumoniae. S. pneumoniae typically produces acute lobar consolidation with higher fevers and productive cough. Influenza can cause systemic symptoms but usually peaks sooner and may precede bacterial superinfection. RSV primarily affects infants and older adults with severe cardiopulmonary disease. Legionella often causes high fever, gastrointestinal symptoms, hyponatremia, and more severe illness.
Further Insight:
- Treat with macrolides or doxycycline (no cell wall).
- Cold agglutinins and bullous myringitis are classic but not required.