Review Question - QID 215063

A 56-year-old man presents to the emergency department with difficulty breathing along with subjective fevers, chills, and a nonproductive cough. The patient states that his symptoms began 4 days ago and have been progressively worsening. He recently returned from a month-long trip to South Africa. He is a longtime smoker with a 30-pack-year history and denies any other drug use. The patient takes atorvastatin for hyperlipidemia and hydrochlorothiazide for hypertension. His temperature is 101.3°F (38.5°C), blood pressure is 135/85 mmHg, pulse is 84/min, respirations are 20/min, and pulse oxygen saturation is 94% on room air. Physical exam shows dullness to percussion at the right posterior base. A chest radiograph reveals blunting of the right costophrenic angle. Pleural fluid analysis from his thoracentesis is as follows:

Serum:
Protein: 5.4 g/dL
Lactate dehydrogenase (LDH): 215 U/L

Pleural:
Protein: 3.1 g/dL
LDH: 90 U/L
Lymphocytes: 86%
Neutrophils: 10%

Which of the following is the most likely etiology of this patient’s symptoms?