Molecular epidemiology and clinical characteristics of hetero-resistant vancomycin intermediate Staphylococcus aureus bacteremia in a Taiwan Medical Center

BackgroundHetero-resistant vancomycin intermediate Staphylococcus aureus (hVISA) emerges worldwide in recent decade. The purpose of this study was to investigate the glycopeptide usage trend, the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) with reduced vancomycin susceptibility, the susceptible rates to newer antimicrobials, molecular epidemiology, clinical characteristics, as well as patient outcome among S. aureus bacteremia cases in a Taiwanese medical center.MethodsFrom March to December 2009, among 118 S. aureus blood isolates in a Taiwanese medical center, 62 MRSA isolates were screened for hVISA by Etest macromethod and further confirmed with modified population analysis profiling method. Molecular typing of hVISA isolates was performed.ResultsFive (4.2%) isolates were hVISA. Compared with non-hVISA MRSA, hVISA isolates had higher resistant rates to ciprofloxacin, gentamicin, trimethoprim/sulfamethoxazole, and tetracycline. Among the MRSA infected, patients infected with hVISA had a higher in-hospital mortality rate than non-hVISA group (60% vs. 17.5%, p = 0.025). All hVISA isolates were nosocomial and had different pulsed field gel electrophoresis pulsotype. Four hVISA isolates carried type III staphylococcal cassette chromosome mec (SCCmec) and the remaining isolate carried SCCmec type II. Three of the 5 hVISA isolates belonged to sequence type 239, which is the most common type in Taiwan. Glycopeptide usage increased in the study hospital; however, these hVISA-infected patients did not receive glycopeptide treatment in the recent 6 months.ConclusionOur results suggested hVISA might have disseminated in the hospital before we observed this highest hVISA rate in Taiwan and increasing glycopeptide usage might serve as selection pressure. Measures to prevent the transmission of MRSA with reduced vancomycin susceptibility and to treat such infection were urgently needed.