A 40-year-old alcoholic develops cough and fever. Chest x-ray, shown below, shows an air-fluid level in the superior segment of the right lower lobe.
Which of the following is the most likely etiologic agent?A. Streptococcus pneumoniae
The chest x-ray shows a pulmonary abscess in the right lower lobe with an air-fluid level. This is characteristic of an anaerobic infection. These are usually associated with a period of loss of consciousness and with poor oral hygiene. The location of the infiltrate suggests aspiration, also making anaerobic infection most likely. The superior segment of the right lower lobe is the segment most likely to develop aspiration pneumonia. Lung abscess indicates a necrotizing process, which is uncommon with the “typical” bacterial pathogens pneumococci and H influenzae, and very rare in the usually patchy “atypical” pneumonias caused by Legionella and Mycoplasma.