Comparative analysis of clinical outcomes in non-fermenting gram-negative bloodstream infections: Stenotrophomonas maltophilia versus Pseudomonas aeruginosa and Acinetobacter baumannii in Asian Tertiary Care

Global antimicrobial resistance (AMR) frameworks prioritise organisms with high acquired resistance, yet intrinsically resistant pathogens may be under-recognised in empiric treatment pathways. Stenotrophomonas maltophilia is intrinsically carbapenem-resistant and may be less visible to carbapenem-centred empiric regimens targeting acquired Gram negative resistance. We conducted a retrospective cohort study at Singapore General Hospital (January 2018–June 2025) of adults with monomicrobial bacteraemia with the non-fermenting Gram-negative bacteria: Pseudomonas aeruginosa, Acinetobacter baumannii, or S. maltophilia. For S. maltophilia, acquired resistance was defined as non-susceptibility to levofloxacin, cotrimoxazole, or minocycline; for P. aeruginosa and A. baumannii, acquired resistance was defined as non-susceptibility to one or more agents within standard antipseudomonal/antimicrobial categories, in accordance with Clinical and Laboratory Standards Institute (CLSI) breakpoints. Primary outcomes were in-hospital and 1-year mortality and years of potential life lost (YPLL). Associations between appropriate empirical therapy and mortality were estimated using multivariable logistic regression. 901 adults with P. aeruginosa (n = 587), A. baumannii (n = 163), or S. maltophilia (n = 151) bacteraemia were identified. S. maltophilia patients were younger (mean 61.5 years) with higher rates of central venous catheter use (78.1%) and neutropenia (25.2%). Acquired resistance was lowest for S. maltophilia (27.2%) versus A. baumannii (52.1%) and P. aeruginosa (34.2%; p < 0.001). Appropriate empirical therapy rates were 67.5% for S. maltophilia, 62.6% for A. baumannii, and 85.5% for P. aeruginosa (p < 0.001). S. maltophilia demonstrated higher in-hospital mortality (43.0% vs. 29.5–31.3%; p < 0.001) and 1-year mortality (45.7% vs. 34.9–36.2%; p = 0.049). YPLL was substantially greater for S. maltophilia (15.4 years) than other pathogens (p < 0.001). Appropriate empirical therapy was independently associated with lower mortality across all assessed timepoints, with the strongest association observed at 30 days (aOR 0.42, p = 0.002). S. maltophilia bacteraemia is associated with higher in-hospital and 1-year mortality and substantially greater YPLL, compared to P. aeruginosa and A. baumannii. Appropriate empirical therapy was independently associated with reduced mortality across all timepoints and the lower rates of appropriate empirical therapy rates in S. maltophilia are consistent with a contribution from delayed effective therapy to poorer outcomes. Not applicable. 1. Patients with S. maltophilia were younger, more neutropenic and more frequently had higher central venous catheter use than patients with P. aeruginosa or A. baumannii bacteraemia 2. Despite having the lowest prevalence of acquired resistance, S. maltophilia was associated with the highest in-hospital mortality (43.0%), one-year mortality (45.7%), and YPLL (GM 15.4 years). 3. Appropriate empirical therapy was less frequently administered for S. maltophilia (67.5%) than in P. aeruginosa bacteraemia and was independently associated with lower mortality across assessed timepoints. These findings highlight an empirical challenge posed by intrinsically resistant pathogens that may not be adequately reflected in conventional acquired-resistance surveillance. 4. Prospective studies are required to determine whether earlier organism identification or risk-stratified empirical treatment improves clinical outcomes.