Risk stratification and source classification in Staphylococcus aureus bloodstream infections: high mortality linked to mrsa, biomarkers, and treatment efficacy.

UNLABELLED: Staphylococcus aureus bloodstream infection (SAB) carries a high mortality rate. This study aims to develop a source-specific classification framework to guide management and improve outcomes.

METHODS

We conducted a retrospective study of 321 S. aureus bloodstream infection patients (2012-2025), using ROC analysis, survival curves, and SPSS to evaluate 12-month in-hospital mortality and its predictors.

RESULTS

Among 3,516 bloodstream infections, 321 episodes of S. aureus bacteremia (SAB) were identified (9.12%). The median time to positivity was 14 hours. The most common infection sources were the lungs (26.8%), catheter-related infections (24.3%), and skin/soft tissue infections (23.4%). Hemodialysis was the predominant comorbidity (21.2%). Biomarker analysis showed high diagnostic accuracy for PCT (AUC 0.957), WBC (AUC 1.000), and neutrophil percentage (AUC 0.913). MRSA accounted for 38% of isolates. Both MRSA and MSSA exhibited >50% resistance to penicillin, erythromycin, and clindamycin, but none to linezolid, vancomycin, or tigecycline. Overall, in-hospital mortality was 30.2%, significantly higher in MRSA (38%) than in MSSA (26%) (p=0.048). Notably, 36.1% of deaths occurred within 24 hours, and 58.7% within 7 days. The 10-day survival rate was lower in MRSA (0.609 vs. 0.759, p=0.029). Healthcare-associated infections (58%) showed no significant association with MRSA prevalence after Bonferroni correction. Independent mortality predictors included qSOFA score ≥2 (OR 3.450, 95% CI 1.835-6.835, p<0.001), age ≥60 years (OR 2.654, 95% CI 1.628-4.327, p<0.001), pulmonary source of BSI (OR 2.362, 95% CI 1.407-3.963, p<0.001), neutrophil percentage ≥89.60% (OR 2.195, 95% CI 1.294-3.720, p=0.003), procalcitonin ≥1.84 ng/mL (OR 2.152, 95% CI 1.210-3.824, p=0.008), ineffective or no antibiotic use (OR 2.359, 95% CI 1.176-4.730, p=0.008), and MRSA infection (OR 1.756, 95% CI 1.081-2.853, p=0.023).

CONCLUSION

This study establishes high-accuracy biomarkers (PCT/WBC) and key mortality predictors for S. aureus BSIs, including MRSA infection, qSOFA≥2, and ineffective antibiotics. These findings enable early risk stratification and emphasize the source-specific classification for prompt, appropriate antimicrobial therapy to improve clinical outcomes.