Diagnostic testing to establish a microbial cause is helpful in the management of community-acquired pneumonia

Antibiotic treatment for community-acquired pneumonia (CAP) can be specifically directed at an identified etiologic agent, or empirically formulated based on consideration of the likely pathogens according to the patient's age, underlying diseases, and clinical presentation. In recent years the empirical approach has become increasingly popular, and there is a growing trend away from efforts to make a microbiological diagnosis. This article reviews the tests that are currently available for the diagnosis of CAP, including stains, cultures, antigen-detection techniques, nucleic acid amplification, and serologies. Arguments then are presented in support of efforts to make a microbiological diagnosis. Clinical and radiographic features of CAP are not sufficiently distinctive to infer a specific microbial cause. Identification of the etiologic agent can be made in the majority of cases, and most microbiological diagnoses can be made rapidly with simple tests. The best opportunity to make an etiologic diagnosis is before antibiotics are administered. Identification of the microbial cause of pneumonia permits specific, narrow-spectrum antibiotic treatment that may be more effective, less toxic, and less expensive than empiric therapy. Microbiological data from individual patients contributes to understanding the local microbial epidemiology of CAP, including the local distribution of pathogens and their antimicrobial resistance patterns, information that is invaluable in the construction and modification of empiric treatment regimens. The reliance on empiric treatment engenders a false complacency, based on the erroneous assumption that broad-spectrum antibiotics will treat all cases of CAP. The unnecessary use of broad-spectrum antibiotic combinations in the empiric treatment of CAP contributes to the growing problem of antimicrobial resistance.