ROLE OF THE MICROBIOLOGY LABORATORY IN THE DIAGNOSIS OF LOWER RESPIRATORY-TRACT INFECTIONS

The appropriate use of the clinical microbiology laboratory for diagno sing lower respiratory tract infections is controversial. As in clinic al care, it is crucial to categorize the presenting illness properly a s acute bronchitis, an acute exacerbation of chronic bronchitis, commu nity-acquired pneumonia, or nosocomial pneumonia if diagnostic efforts to establish a microbial etiology are to be productive for the indivi dual patient and affordable to society. The greatest potential benefit of microbiological investigations lies in the etiologic diagnosis of pneumonia. For community-acquired pneumonia, evaluation of a gram-stai ned smear of sputum in terms of both quality and microorganisms presen t can help guide initial therapy as well as aid interpretation of subs equent culture results. As discussed in this review, the role of the c linical microbiology laboratory in the etiologic diagnosis of nosocomi al and complicated pneumonias is more extensive and, in addition to ev aluation of respiratory secretions, may include cultures of blood, ple ural fluid, and specimens obtained by bronchoscopy. However, a prerequ isite for the use of all currently available tests is their deployment for patients with clinical and radiographic evidence of pneumonia.