Nosocomial pneumonia in mechanically ventilated adult patients: epidemiology and prevention in 1996.

Mechanically ventilated patients have a higher incidence of pneumonia and mortality than do nonventilated patients. Ventilator-associated pneumonia (VAP) is diagnosed clinically, by bronchoscopy or "blind" bronchoalveolar lavage (BAL) or protected specimen brush (PSB), and by quantitative endobronchial aspirates (QEA). VAP is usually caused by bacteria, but Legionella pneumophila, Mycobacterium tuberculosis, viruses, and fungi are also potential pathogens. Bacteria causing nosocomial pneumonia may be part of the patient's endogenous flora, originate from other patients, hospital personnel, or environmental sources. Pseudomonas aeruginosa, Acinetobacter spp, and Staphylococcus aureus are the most common causative agents in late-onset nosocomial pneumonia, and Streptococcus pneumoniae and Hemophilus influenzae are more commonly found in early-onset pneumonia. Aspiration appears to be the major route for the entry of bacteria into the lower respiratory tract. Host factors, oropharyngeal and gastric colonization, cross-infection, and complications from the use of antibiotics and nasogastric and endotracheal tubes increases the risk of bacterial VAP. A working knowledge of the epidemiology and strategies for prevention of VAP should reduce infection rates, morbidity, and mortality in critically ill patients.