Elevated vancomycin minimum inhibitory concentrations among methicillin-resistant Staphylococcus aureus isolated from...

Emerging evidence suggests that vancomycin minimum inhibitory concentrations (MICs) within methicillin-resistant Staphylococcus aureus (MRSA) are increasing. The objective of this surveillance study was to determine vancomycin MIC distributions for MRSA isolates collected from the respiratory tract of patients with ventilator-associated pneumonia (VAP) at a large community hospital in Hartford, Connecticut. The frequency of heteroresistant vancomycin intermediate S. aureus (hVISA) was also assessed for select isolates. Vancomycin MICs and hVISA screening were conducted using standard inoculum and macromethod Etest methodology, respectively, for isolates collected between November 2005 and August 2007. Fifty-eight isolates of MRSA were collected over the two-year period. The MIC50 and MIC90 were both 2 microg/ml; 31.0% and 58.6% of isolates had vancomycin MICs of 1.5 microg/ml and 2 microg/ml, respectively. None of the isolates tested were positive for hVISA; four isolates were VISA. Vancomycin MICs for respiratory MRSA at this Connecticut hospital are elevated. Institution-specific surveillance in the state is warranted.