The Clinical and Prognostic Importance of Positive Blood Cultures in Adults

Abstract

Background Bloodstream infections are a major cause of morbidity and mortality in adults. Bloodstream infections should be reassessed periodically because of increased antibiotic resistance, more patients receiving immunomodulatory therapy, improved antiretroviral therapy, and acquisition of infection in health care settings other than hospitals. Methods We conducted retrospective assessment by infectious disease physicians of hospitalized adults with positive blood cultures at 3 academic medical centers. Results Two thousand two hundred seventy positive blood culture episodes occurred in 1706 patients. Of 2669 isolates, 51% represented true infection, 41% contamination, and 8% unknown clinical significance. Although coagulase-negative staphylococci were most common, only 10% were clinically significant. Among 1225 true bloodstream infections, the most frequent isolates were Staphylococcus aureus, Escherichia coli, Enterococcus spp., Klebsiella pneumoniae, coagulase-negative staphylococci, Pseudomonas aeruginosa, Candida albicans, Enterobacter cloacae, and Serratia marcescens. Intravenous catheters were the most common primary source of bloodstream infection (23% of episodes). Most (81%) bloodstream infections were acquired in the hospital or other health care settings. Crude and attributable in-hospital case-fatality ratios were 20% and 12%, respectively, lower than in previous studies. Increasing age, hypotension, absence of fever, hospital acquisition, extreme white blood cell count values, and the presence of the acquired immunodeficiency syndrome, malignancy, or renal disease were significantly associated with an increased risk of in-hospital attributable death in multivariable analysis. Conclusions The proportion of bloodstream infections due to intravenous catheters is continuing to increase. Most episodes were acquired in the hospital or other health care setting. In-hospital case-fatality ratios have decreased compared with previous studies. Several previously identified factors associated with an increased mortality remain statistically significant.