Incidence, etiologic pathogens, and diagnostic testing of community-acquired pneumonia.

Determination of the etiologic pathogens of community-acquired pneumonia has been problematic because of the lack of reliable rapid laboratory diagnostic tools as well as the controversy concerning diagnostic criteria. In the studies reviewed here, a specific pathogen was identified in 39% to 88% of patients. Streptococcus pneumoniae remains the most common cause of community-acquired pneumonia. Depending on the demographics of the study, between 2% to 43% of cases have been attributed to legionella or Chlamydia pneumoniae. More recently, other pathogens have emerged, including respiratory syncytial virus in adults, hantavirus, and possibly legionella-like amoebal pathogens and Streptococcus milleri group. Treatment guidelines published by various societies of experts have been helpful, but they cannot replace the need for better and rapid diagnostic techniques.