Utility of Blood Cultures in Pneumonia

Abstract

Introduction: Blood cultures are of limited utility in nonsevere community-acquired pneumonia, though routinely recommended for severe community-acquired pneumonia or health care-associated pneumonia due to perceived greater bacteremia risk, particularly with multidrug-resistant organisms. The utility of this practice is unknown. Methods: In this observational cohort study, we abstracted data from medical records for consecutive hospitalizations for pneumonia by adults to an academic medical center from 2014-2015. The primary outcomes included bacteremia, multidrug-resistant organism bacteremia, and appropriate management changes attributed to culture results, stratified by pneumonia classification (nonsevere community-acquired pneumonia, severe community-acquired pneumonia, or health care-associated pneumonia) and likelihood the bacteremia was due to pneumonia vs another infection. We assessed the diagnostic test performance of one or more guideline-defined risk factors for bacteremia in nonsevere community-acquired pneumonia, for whom cultures are routinely recommended. Results: Of 456 pneumonia hospitalizations, 30 (6.6%) had bacteremia, with a greater incidence in severe community-acquired pneumonia (14.7%) than nonsevere community-acquired pneumonia (7.8%) and health care-associated pneumonia (6.6%; P = .12). Seventeen bacteremia cases were likely due to pneumonia (3.7%). Only 2 (0.4%) had multidrug-resistant organisms (both health care-associated pneumonia), one of whom was due to pneumonia. Appropriate management changes occurred in 8 cases (1.8%; 7 de-escalation and 1 escalation of antibiotics); only 1 with bacteremia likely due to pneumonia (de-escalation). The one case of appropriate antibiotic escalation occurred in a patient with vancomycin-resistant Enterococcus unrelated to pneumonia. Having one or more guideline-defined risk factors did not identify bacteremia in nonsevere community-acquired pneumonia (positive likelihood ratio, 1.10; 95% confidence interval, 0.61-1.99). Conclusion: Routine blood cultures in pneumonia have extremely low yield and utility irrespective of severity and risk.