Ventilator-associated bacterial pneumonia: challenges in diagnosis, treatment, and prevention.

Ventilator-associated pneumonia (VAP) is a common infection in intensive care unit patients that results in high mortality and morbidity and increased duration of hospital stay. Clinical diagnostic methods are sensitive, but lack specificity. Quantitative analysis of specimens from the lower respiratory tract increases specificity. Bacteria causing VAP may originate from the patient's endogenous flora, other patients or hospital personnel, or from environmental sources. Aspiration or direct inoculation are the major routes of bacterial entry into the lower respiratory tract. The bacterial inoculum and host response in the lung are important factors for pathogenesis. Late-onset nosocomial pneumonia is often caused by Pseudomonas aeruginosa, Acinetobacter species, and Staphylococcus aureus. Streptococcus pneumoniae and Haemophilus influenzae, however, are the more common pathogens in early-onset disease. Oropharyngeal and gastric colonization with bacteria, cross-infection, as well as the indiscriminate use of antibiotics or invasive devices substantially increase the risk of VAP. An understanding of the epidemiology and pathogenesis of VAP, along with implementation of appropriate preventive measures, are needed to decrease the incidence, morbidity, and mortality associated with VAP.