Clinical, microbiological, and molecular characteristics, outcomes, and risk factors for mortality of patients with Stenotrophomonas maltophilia bloodstream infection

Abstract Purpose The aim of this study was to explore the clinical, microbiological, and molecular characteristics of Stenotrophomonas maltophilia bacteraemia, outcomes, and risk factors associated with mortality. Methods This was a nationwide retrospective cohort study of patients with S. maltophilia bacteraemia during the period between January 2017 and December 2021. MIC Test Strips (Liofilchem, Roseto degli Abruzzi, Italy) were used for susceptibility testing, and Illumina for whole genome sequencing. Kaplan–Meier survival analysis and a multivariable Cox regression model were utilized to assess independent predictors of 90-day all-cause mortality. Results Ninety patients were included, with a median age of 51.5 years (IQR 37–61), and 25.6% were females. The most common underlying medical conditions included diabetes mellitus (42.2%), and haematological malignancy (23.3%); and 64.4% were immunosuppressed. The most common sources of bacteraemia were the respiratory tract (38.9%) and vascular lines (25.6%). In vitro susceptibility rates were highest for trimethoprim-sulfamethoxazole (98.9%), and levofloxacin (61.1%). Sequencing demonstrated extensive genomic heterogeneity, and sul1 gene was detected in only one strain. The most frequent therapy was trimethoprim-sulfamethoxazole, monotherapy (77.8%) or in combinations (6.7%), for a median duration of 10 days (IQR 5–14). All-cause 90-day mortality was 44.4%. Receiving trimethoprim-sulfamethoxazole was associated with improved 90-day survival (log-rank P < 0.001), and was independently associated with lower mortality in the multivariable Cox model (hazard ratio 0.21, 95% confidence interval 0.06 to 0.74). Conclusion S. maltophilia blood isolates are genomically diverse and remain mostly susceptible to trimethoprim-sulfamethoxazole. Using trimethoprim-sulfamethoxazole for patients with S. maltophilia bacteraemia appears to be associated with improved survival.