Severe community-acquired pneumonia.

Community-acquired pneumonia (CAP) is likely to be severe in the very elderly, and clinically significant in those with hepatic/ renal insufficiency, cardiopulmonary disease, or, impaired host defenses. Pathogens in mild, moderately severe, and severe CAP are the same. These pathogens determine prognosis, complications, and duration of therapy. Empiric antimicrobial therapy should be based on likely pathogens, not severity of illness which affects the potency but not spectrum of antibiotic selected.