The second most common
nosocomial infection in the United States is
pneumonia, with the highest rates seen in patients requiring
mechanical ventilation.
Nosocomial pneumonia is a serious disease associated with significant morbidity and mortality; crude mortality rates have been estimated at 20% to 50%. The rapid institution of appropriate antimicrobial
therapy has been shown to improve mortality in patients with
ventilator associated
nosocomial pneumonia. Thus, the identification of
nosocomial pneumonia with a timely microbiologic diagnosis is important for the management of these patients. However, the accurate diagnosis of
nosocomial pneumonia, along with identification of the responsible organism(s), can be challenging. This task becomes even more difficult in patients who are mechanically ventilated. The presence of new pulmonary infiltrates along with clinical criteria including
fever,
cough, and purulent secretions are neither sensitive nor specific for the diagnosis of
nosocomial pneumonia. The laboratory can enhance the accuracy of
pneumonia diagnosis, as well as provide the identification of an etiologic organism(s). There are, however, many challenges which confront the laboratory including: the ability to identify organisms from an extensive microbiologic spectrum; distinguishing colonization from
infection of predominately gram-negative oropharyngeal flora; and providing timely results. This article reviews the various diagnostic tests available for nosocomial lung
infections, and in particular,
ventilator associated pneumonia including: blood cultures; pleural fluid; expectorated sputum; endotracheal aspirates; and respiratory specimens obtained by more invasive techniques using bronchoscopy and transthoracic needle aspiration. Emphasis is placed on optimal specimen collection, the processing of samples in the laboratory, and on the evaluation of potential risks and benefits associated with the varying techniques.