Nosocomial lung infection and its diagnosis

Nosocomial pneumonia occurs in 0.5% to 5.0% of all hospital admissions and is responsible for 15% of hospital deaths. Up to 60% of ICU patients may develop pneumonia, depending on the severity of their underlying disease. Despite the availability of potent antibiotics, ICU patients who develop Gram-negative pneumonia have a disturbingly high mortality rate. Specific etiologic diagnosis is frequently lacking because microbiological samples are commonly contaminated by oropharyngeal secretions which are colonized by Gram-negative bacilli (GNB) in up to 100% of ICU patients. Great controversy surrounds the value of various methods used to diagnose nosocomial pneumonia. Clinical criteria of pneumonia include fever, leukocytosis, purulent tracheobronchial secretions, and a new infiltrate on chest x-ray--all of which are also frequently observed in patients free of pneumonia. Tracheobronchial secretions are often contaminated by microorganisms colonizing the upper airways and their examination may provide misleading information and result in patient mismanagement. Blood cultures are valuable but positive in only a small proportion of patients with nosocomial pneumonia. Transtracheal and transthoracic aspiration are unsatisfactory in the intubated patient requiring mechanical ventilation. Immunologic techniques like countercurrent immunoelectrophoresis are promising but presently inadequate to screen for a wide variety of organisms. Transbronchial or open-lung biopsy may be considered if the pneumonia is thought to be due to opportunistic organisms rather than bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)