A 27-year-old man presents to clinic for assessment of new left-sided chest pain and feeling unwell. He describes developing a new cough with some blood-tinged sputum, fever, and chills of 2 days duration. His past medical history is negative, and he reports smoking about 1 pack a day. On physical examination, the pertinent findings are dullness and crackles in the left lower chest. His CXR is shown in Figure below. Which of the following is the most likely diagnosis?
High-Yield Explanation
The diagnosis is pneumonia. There is consolidation of the left lower lobe. The increased density, presence of air bronchogram, and the silhouetting of the left diaphragm point to a parenchymal lesion. Pneumococcal infection, as in this patient, is still the most common etiology, although other bacterial infections such as Klebsiella, Streptococcus, or, Staphylococcus is often encountered. Viral and arthropod-borne diseases are also seen.