SAN FRANCISCO — Physicians who forgo obtaining cultures from patients who come in with possible community-acquired bacterial pneumonia are probably practicing wisely, John G. Bartlett, M.D., said at the annual meeting of the American College of Physicians.
Culturing pneumonia is an uncertain proposition. It has been reported that the etiologic agent is never identified in 50% of cases. But that figure comes from clinical trials, in which patients are tested exhaustively, said Dr. Bartlett, chief of the division of infectious diseases at Johns Hopkins University, Baltimore.
In the hospital, the etiologic organism is identified in only 15%–20% of pneumonia cases, and most results come from blood culture, not sputum. Sputum rarely yields a positive culture, even in a patient with a pneumonia caused by Streptococcus pneumoniae.
Blood cultures may provide misleading results because the cultures are often contaminated, Medicare data suggest. “There have been several reports that have shown that blood cultures really don't affect outcome in any meaningful way,” Dr. Bartlett said.
Current guidelines say that when diagnosing suspected pneumonia from bronchitis, an x-ray is key, although an x-ray is not needed in the patient with normal vital signs and no rales.
If the x-ray shows an infiltrate, then the patient has pneumonia, and antibiotic treatment can be initiated empirically, with no need for a culture, because experience suggests that most patients get better with empiric treatment, Dr. Bartlett said.
The exception to this empiric-treatment rule would be for the patient who is ill enough to be hospitalized, Dr. Bartlett said. In those patients, he would order a urinary antigen test for Legionella.