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Prior vancomycin use is a risk factor for reduced vancomycin susceptibility in methicillin-susceptible but not

Kara B Mascitti1, Paul H Edelstein, Neil O Fishman

  • 1Division of Infectious Diseases, Department of Medicine, St. Luke's Hospital and Health Network, Bethlehem, Pennsylvania, USA. mascitk@slhn.org

Infection Control and Hospital Epidemiology
|January 10, 2012
PubMed
Abstract

Insights

Reduced vancomycin susceptibility (RVS) in Staphylococcus aureus bacteremia is common. Prior vancomycin use was linked to RVS in methicillin-susceptible S. aureus (MSSA) but not methicillin-resistant S. aureus (MRSA) infections.

Area of Science:

  • Infectious Diseases
  • Clinical Microbiology
  • Antimicrobial Resistance

Background:

  • Staphylococcus aureus causes significant community- and healthcare-acquired infections.
  • Increasing vancomycin minimum inhibitory concentrations (MICs) in S. aureus raise concerns about treatment efficacy.
  • Reduced vancomycin susceptibility (RVS) in S. aureus may correlate with treatment failures.

Purpose of the Study:

  • To identify clinical risk factors associated with RVS in S. aureus bacteremia.
  • To investigate the relationship between prior vancomycin use and RVS in S. aureus bacteremia.
  • To explore potential differences in RVS risk factors between methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) infections.

Main Methods:

  • A case-control study design was employed.
  • Patients with RVS S. aureus isolates (vancomycin E-test MIC >1.0 μg/mL) were cases, and those with non-RVS isolates were controls.
  • Data were collected from an academic tertiary care medical center and an affiliated urban community hospital.

Main Results:

  • Out of 392 subjects, 134 (34.2%) exhibited RVS.
  • RVS prevalence was 28.7% in MSSA and 40.0% in MRSA (P = .02).
  • Prior vancomycin use was associated with RVS (OR, 2.08). This association was significant for MSSA (adjusted OR, 4.02) but not MRSA (adjusted OR, 0.87) after controlling for other factors.

Conclusions:

  • A significant proportion of S. aureus bacteremia cases demonstrated RVS.
  • The association between prior vancomycin use and RVS differs between MSSA and MRSA infections.
  • These findings suggest a complex interplay between clinical factors and the molecular epidemiology of RVS in S. aureus.

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