Community-onset Anaerobic Bloodstream Infection, Predisposing Factors, and Impact on Survival: A Prospective Cohort Study

Background: Few studies have examined the outcomes and predisposing risk factors for anaerobic bloodstream infections (BSIs).Objective: To determine the survival impact of aerobic versus anaerobic BSI, a prospective cohort study was conducted.Methods: We prospectively enrolled emergency department patients at a tertiary medical center with BSIs determined by laboratory testing between 2015 and 2016. Anaerobic and aerobic BSIs were compared for de-mographics, comorbidities, and sources of infection. Several independent risk factors were identified in a multivariable logistic regression model. Using propensity score (PS) matched data, an analysis of survival effects associated with anaerobic BSI has been conducted.Results: Over a 2-year period, there were 1,166 episodes of BSI, of which 61 (5.2%) occurred as anaerobic ep-isodes. Anaerobic BSIs were strongly associated with intra-abdominal infection (odds ratio [OR] 6.03, 95%CI 2.78-13.09), liver abscess (OR 3.92, 95%CI 1.47-10.45), skin and soft-tissue infection (OR 2.65, 95%CI 1.26-5.62), and metastatic cancer (OR 2.40, 95%CI 1.13-5.08) as the main positive predictors. Negative pre-dictors included diabetes mellitus (OR 0.38, 95%CI 0.18-0.78), thrombocytopenia (OR 0.33, 95%CI 0.18-0.60), and urinary tract infection (OR 0.15, 95%CI 0.04-0.62). Anaerobic BSIs were not associated with worse prog-nosis after PS-matched analysis (hazard ratio [HR] 1.40, 95%CI 0.44-4.41) in our cohort.Conclusions: A significant percentage of community-onset BSI was due to anaerobic BSI. Anaerobic BSI can have a detrimental outcome if there are underlying comorbidities, high-risk infection sites, and inappropriate antibiotic choices. The findings of our study may contribute to the prescription of empiric anti-anaerobe antibiotics.