A 34-year-old man fell ill 3 days ago after an overexposure to cold. He complains of a fever of 39.2°C, marked general weakness, sweating, and cough. The cough was initially dry, but within the last 24 hours a small amount of "rusty" sputum was produced. Objective examination detects herpes on the lips. Percussion reveals a dull sound in the lower pulmonary lobes. Auscultation detects bronchial breathing and tachycardia. No changes were detected in the organs of the abdominal cavity. What is the most likely diagnosis in this case