Emerging pathogens in nosocomial pneumonia.

The organisms responsible for nosocomial pneumonia are continuously evolving. Gram-negative bacilli have become the most common etiologic agents over the past 20 years, and with this evolution has come a better understanding of the pathogenesis of gram-negative bacillary pneumonia. Some gram-positive cocci, such as enterococci, group B beta hemolytic streptococci and methicillin-resistant Staphylococcus aureus, haven taken on new significance in nosocomial respiratory infections. Streptococcus pneumoniae, nontypeable Haemophilus influenzae and Branhamella catarrhalis are increasingly reported in hospitalized patients with chronic lung disease. Etiologic agents will change as new antibiotics are introduced. A better understanding of etiologic agents and their pathogens may be the best tool toward preventing hospital-acquired pneumonia.