Community-Acquired Pneumonia, Bacterial

File, Thomas M.

Abstract Community-acquired pneumonia (CAP) is defined as an acute infection of the pulmonary parenchyma in a patient who has acquired the infection in the community and has not had recent hospitalization or association with other healthcare facilities such as nursing homes, dialysis centers, and outpatient clinics. CAP is a common and potentially serious illness, particularly in elderly patients and those with significant comorbidities. CAP may be caused by myriad pathogens, but bacteria are the most common causes. Bacteria have traditionally been divided into two groups: typical and atypical agents. Typical organisms include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, group A streptococci, Moraxella catarrhalis, anaerobes, and aerobic gram-negative bacteria. Atypical organisms include Legionella species, Mycoplasma pneumoniae, Chlamydophila (also known as Chlamydia) pneumoniae, and Chlamydophila psittaci. This chapter will focus on the general approach to CAP in adults, with a concentration primarily on typical bacterial causes. Other chapters focus specifically on pneumonia caused by aspiration, viruses, or atypical organisms.