Clinical and microbiologic analysis of the risk factors for mortality in patients with heterogeneous vancomycin-intermediate Staphylococcus aureus bacteremia

Abstract

The prevalence of the heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) phenotype among methicillin-resistant S. aureus (MRSA) blood isolates can reach 38%. hVISA bacteremia is known to be associated with vancomycin treatment failure, including persistent bacteremia. We conducted this study to evaluate risk factors for 12-week mortality in patients with hVISA bacteremia through a detailed clinical and microbiological analysis of a prospective cohort of patients with S. aureus bacteremia. All isolates were collected on the first day of bacteremia and subjected to population analysis profiling for hVISA detection, genotyping, and PCR analysis for 39 virulence factors. Of 382 patient with MRSA bacteremia, 121 (32%) had hVISA bacteremia. Deceased patients were more likely to have hematologic malignancy (P = 0.033), ultimately or rapidly fatal disease (P = 0.007), and a higher Pitt bacteremia score (P = 0.010) than surviving patients. The sequence type 239 (ST239) clonal type and definitive linezolid treatment were associated with a trend toward reduced mortality (P = 0.061 and 0.072, respectively), but a high vancomycin MIC (≥2 mg/liter) was not associated with increased mortality (P = 0.368). In a multivariate analysis, ultimately or rapidly fatal disease (adjusted odds ratio [aOR], 2.80; 95% confidence interval [CI], 1.14 to 6.85) and a high Pitt bacteremia score (aOR, 1.26; 95% CI, 1.07 to 1.48) were independent risk factors for mortality. Hematologic malignancy was associated with a trend toward increased mortality (P = 0.094), and ST239 was associated with a trend toward reduced mortality (P = 0.095). Our study suggests that ST239 hVISA is a possible predictor of survival in hVISA bacteremia.