Community-acquired pneumonia in adults.

The most common etiologic agent of CAP is Streptococcus pneumoniae. Atypical pathogens are the cause in approximately 20% to 30% of patients. Because the patients clinical presentation cannot be used to predict if a patient is infected with S. pneumoniae or an atypical pathogen, the initial empiric therapy should cover for these core organisms in all patients. In patients with CAP, the antibiotic spectrum of initial empiric therapy will escalate from an oral macrolide in an ambulatory patient without risk factors for resistant pathogens, to intravenous combination therapy, in a hospitalized patient in the intensive care unit with risk factors for resistant gram-negative organisms. The hospitalized patient can be switched safely from intravenous to oral therapy once he or she reaches clinical stability. The use of pneumococcal vaccine, influenza vaccine, and smoking-cessation programs is an important strategy to prevent CAP.