Review Question - QID 214913

A 67-year-old man presents to the emergency department with fever, shortness of breath, and cough, which has worsened over the course of 1 week. He endorses mild chest pain and denies any palpitations or hemoptysis. He denies any recent travel or sick contacts. He has had 4 similar presentations over the course of the past year and was successfully managed with intravenous antibiotics. His medical history is otherwise notable for hypertension, hyperlipidemia, and gastroesophageal reflux disease for which he takes lisinopril, atorvastatin, and omeprazole. The patient has smoked 1 pack of cigarettes daily for the past 40 years. His temperature is 101°F (38.3°C), blood pressure is 145/80 mmHg, pulse is 86/min, respirations are 18/min, and oxygen saturation is 93% on pulse oximetry. Radiography of the chest demonstrates a right middle lobe opacity, which is similar to his radiographs from his prior hospitalizations. Which of the following diagnostic studies is the most appropriate to confirm the underlying cause of this patient's symptoms?