Clinical and Genomic Characterization of Serratia Bloodstream Infections

Previously considered a rare opportunistic pathogen, Serratia is now an emerging cause of bacteremia. We compared the risk factors and outcomes of patients with Serratia bacteremia relative to other Enterobacterales in a cohort of hospitalized patients.

Patients were prospectively enrolled from 2002-2021 at Duke University. Characteristics and outcomes were compared among bacteremic patients due to Serratia and other Enterobacterales. Regression models were used to determine features associated with outcomes. Whole genome sequencing (WGS) was performed to characterize the phylogenetic diversity of Serratia isolates associated with device infections.

Of 2676 patients, 173 (6.5%) had Serratia bacteremia. Among patients with a medical device (n = 993; 37.1%), Serratia was associated with an increased risk of device infection in an adjusted model (odds ratio (aOR) 2.03; 95% confidence interval (CI), 1.23-3.34). Device infection risk was highest among patients with cardiac devices (OR 3.95, 95% CI 1.45-10.75). Serratia was associated with a greater risk of persistent bacteremia (aOR 1.66, 95% CI 1.08-2.54). WGS of Serratia isolates (n = 93) revealed considerable genetic diversity, with no association between phylogenetic clusters and device infections overall (P = 0.35) or cardiac device infections specifically (P = 0.13).

Compared to other Enterobacterales, patients with Serratia bacteremia were more likely to have a device infection in general, a cardiac device-associated infection in particular, and persistent bacteremia. WGS demonstrated genomic diversity of S. marcescens isolates, suggesting the molecular basis for device infection is not clonal. Further studies are needed to elucidate the mechanism underpinning this finding.