Community-acquired pneumonia: an approach to antimicrobial therapy.

Community-acquired pneumonia (CAP), the sixth leading cause of death in the United States, has undergone significant changes in the past 30 years. In addition to the fact that it increasingly is a disease affecting the elderly and those patients with underlying comorbidities, the spectrum of microbiological agents causing pneumonia has greatly expanded and includes in addition to Streptococcus pneumoniae many other agents including Mycoplasma, Chlamydia, and respiratory viruses. A major problem encountered by the clinician facing a patient with CAP derives from the imprecise clinical presentation, which in most instances does not permit a precise diagnosis of the etiological agent. As pneumonia, if untreated, is frequently a rapidly progressive illness, the clinician usually chooses antimicrobial agents on an empirical basis. Careful attention to historical, physical, and laboratory findings, as well as age and presence of comorbidities has led to a categorization of CAP into four groupings that assist in deciding whether the patient should be hospitalized and what empirical antimicrobial regimen should be started. Careful follow-up and familiarity with the clinical pneumonic syndromes associated with different microbial agents is essential to assure a successful outcome.