Diagnostic test for etiologic agents of community-acquired pneumonia

Diagnostic tests for the detection of the etiologic agent of pneumonia are neither recommended nor done for most outpatients with CAP (Table 4). Most of these patients have no clear diagnosis but seem to do well with empiric antibiotic treatment, which often costs less than the diagnostic tests. For hospitalized patients, a pre-treatment blood culture and an expectorated sputum gram stain and culture should be done. Testing for Legionella spp is appropriate in hospitalized patients, especially those who are seriously ill. New tests that merit use in selected patients are the urinary antigen assay for S pneumoniae and the PCR test for L pneumophila. Anticipated developments in the near future are PCR tests for detection of C pneumoniae and M pneumoniae.