CAP is an infection of the pulmonary parenchyma acquired outside of a health care setting. CAP is common, with more than 1.5 million adults hospitalized annually, and is the most common infectious cause of death in the US.1
CAP is a heterogeneous illness, both in illness severity and pathogens. The most common bacterial pathogens are Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, S aureus, Legionella species, Chlamydia pneumoniae, and Moraxella catarrhalis. However, the microbiologic etiology of CAP is evolving, with increasing recognition of the role of viral pathogens using molecular detection methods.