A 27-year-old man presents with chest pain and feeling unwell. He describes cough with blood-tinged sputum, chills, and fever of 2 days' duration. Physical findings reveal dullness and moist rales in the left lower chest. His CXR is shown in Figure given below. Which of the following is the most likely diagnosis?

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.