A Population-Based Evaluation of Polymicrobial Staphylococcus aureus Bacteremia

Objective: To provide an evaluation of incidence and six-month mortality rates of polymicrobial Staphylococcus aureus bacteremia (p-SAB) in the United States (US). Methods: A retrospective population-based study of all incident adults with monomicrobial SAB (m-SAB) and p-SAB in Olmsted County, Minnesota (MN) from 1 January 2006, through 31 December 2020, was conducted. Demographics, clinical characteristics, in-hospital outcomes, and six-month survival were compared between groups. Results: Overall, 31 incident p-SAB cases occurred during the 15-year study period, corresponding to an overall age- and sex-standardized incidence rate of 1.9/100,000 person-years (95% CI, 1.3-2.6). One-third of p-SAB cases were due to MRSA, and almost one-half (15/31) were caused by Gram-positive bacteria. As compared to the 541 cases with incident m-SAB, p-SAB patients were more likely to have a catheter-related infection (p = 0.008) and less likely to be community-acquired cases (p = 0.027). The unadjusted risk of six-month mortality was greater in the p-SAB group (14/31, 45.2%) compared to the m-SAB group (144/541, 26.6%) (HR = 1.94, 95% CI = 1.12-3.36, p = 0.018). After adjusting for relevant covariates, this difference approached significance (HR = 1.93, 95% = CI 0.96-3.87, p = 0.064). Conclusions: To our knowledge, the current investigation represents the only US population-based study evaluating p-SAB patients. We found lower incidence rates for p-SAB than previously reported, with almost one-half of the cases caused by Gram-positive bacteria. Furthermore, these patients had poor survival compared to incident m-SAB cases.