Pneumonia USMLE Step 1 Practice Question
A 65-year-old man with a history of chronic obstructive pulmonary disease is hospitalized following elective abdominal surgery. On postoperative day 8, he develops fever (38.9°C), productive cough with purulent sputum, and progressive hypoxia. Physical examination reveals scattered crackles in the right lower lobe. Vital signs: BP 128/76 mmHg, HR 102 bpm, RR 22/min, SpO2 88% on room air. Laboratory studies show WBC 14,200/μL. Chest X-ray demonstrates a new right lower lobe infiltrate. Sputum culture grows gram-negative rods that are oxidase-positive and resistant to multiple beta-lactam antibiotics, including ceftazidime. Which of the following organisms is most likely responsible for this patient's pneumonia?
Answer choices
- AChlamydia pneumoniae
- BStreptococcus pneumoniae
- CHaemophilus influenzae
- DKlebsiella pneumoniae
- EPseudomonas aeruginosaCorrect answer
- FLegionella pneumophila
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.