The utility of blood culture in patients with community-acquired pneumonia.

Community-acquired pneumonia (CAP) presents both a diagnostic and therapeutic challenge to clinicians. The prognosis of CAP remains poor with a 4% to 33% fatal outcome. Most initial therapy is necessarily empiric because of the nonspecificity of clinical and radiographic findings and the limitations of diagnostic tests. Severity of illness at initial presentation and the presence of either coexisting illness or advanced age influence the spectrum of etiologic agents and the initial approach to therapy. Although an early etiologic diagnosis is optimal in the management of CAP, in as much as 50% of all patients the responsible pathogen is not defined, even with extensive diagnostic testing. The emphasis in the initial diagnostic approach is to not order extensive tests. The practice of obtaining blood cultures seldom leads to alteration in the therapeutic regimen, even if the cultures are positive. Lack of clinical improvement with empiric therapy, complications from unrelated underlying diseases, and allergic reactions are usually stronger forces for determining change in treatment. Requiring blood cultures only for patients with the greatest risk of mortality from bacteremia from pneumonia would save not only the cost of the blood cultures themselves but also costs resulting from contaminants. As a pragmatic approach, a strategy for microbial investigation linked to illness severity is suggested to replace the current haphazard approach.