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.