Impact of vancomycin use trend change due to the availability of alternative antibiotics on the prevalence of Staphylococcus aureus with reduced vancomycin susceptibility: a 14-year retrospective study

Background We investigated the trend change in vancomycin-intermediate Staphylococcus aureus (VISA)/heterogeneous VISA (hVISA) prevalence among methicillin-resistant S. aureus (MRSA) bacteremia strains and antistaphylococcal antibiotic use together with mutation studies of vancomycin resistance-related gene loci to evaluate the impact of changes in antibiotic use after new antistaphylococcal antibiotics became available. Methods Among 850 healthcare-associated MRSA isolates from 2006 to 2019 at a tertiary hospital in South Korea, hVISA/VISA was determined by modified PAP/AUC analysis, and the identified hVISA/VISA strains were genotyped. Gene mutations at vraSR, graSR, walKR, and rpoB were studied by full-length sequencing. Antistaphylococcal antibiotic use in 2005-2018 was analyzed. Results Two VISA and 23 hVISA strains were identified. The prevalence rate ratio of hVISA/VISA carrying mutations at the two-component regulatory systems among MRSA was 0.668 (95% CI 0.531-0.841; P = 0.001), and the prevalence rate ratio of hVISA/VISA carrying rpoB gene mutations was 1.293 (95% CI 0.981-1.702; 174 P = 0.068). Annual vancomycin use density analyzed by days of therapy (DOT) per 1,000 patient-days did not decrease significantly, however the annual average length of time analyzed by the number of days vancomycin was administered for each case showed a significantly decreasing trend. Conclusions During the 14-year period when the average length of vancomycin therapy decreased every year with the availability of alternative antibiotics, the prevalence of hVISA/VISA did not decrease significantly. This seems to be because the resistant strains carrying the rpoB mutations increased despite the decrease in the strains carrying the mutations at the two-component regulatory systems.

Automated summary

The prevalence of vancomycin-intermediate Staphylococcus aureus (VISA)/heterogeneous VISA (hVISA) did not significantly decrease over a 14-year period, despite a decrease in the average length of vancomycin therapy. The increase in strains carrying rpoB gene mutations may be contributing to this trend.