Ninth U.S. Case of Vancomycin-Resistant Staphylococcus aureus — 2007

Vancomycin remains the preferred treatment for severe methicillin-resistant Staphylococcus aureus (MRSA) infections; thus, vancomycin resistance has substantial clinical and public health implications. The ninth U.S. case of vancomycin-resistant Staphylococcus aureus (VRSA) was diagnosed on December 13, 2007 and investigated through March 4, 2008 by the Michigan Department of Community Health.

Patient's medical records were reviewed for demographic, comorbidity, and historical information. Laboratory tests included susceptibility testing (vancomycin resistance: minimum inhibitory concentration (MIC) ≥16µg/mL), polymerase chain reaction (PCR) for van genes encoding vancomycin resistance, and pulsed-field gel electrophoresis (PFGE) for comparison with previous VRSA isolates. Potential contacts were identified, prioritized, and screened for VRSA.

Vancomycin-resistant Enterococcus and VRSA were isolated from the chronic foot ulcers of a patient, aged 54 years, with inadequately controlled insulin-dependant diabetes, and neither a history of long-term vancomycin use nor a history of MRSA infection. The VRSA isolate had a vancomycin MIC = 1,024 µg/mL, was vanA-positive, and had a unique PFGE pattern. From 126 patient contacts, 140 swabs were collected; 40 (32%) contacts were S. aureus-positive. Thirteen (32%) of these were MRSA; none was VRSA.

This case is consistent with the demographics, clinical course, comorbidities, epidemiology and laboratory findings of prior VRSA cases, except that it is the first without documented prior MRSA infection or colonization. Transmission between patients, or to patient contacts, has not been documented. However, lack of documented MRSA and absence of long-term exposure to vancomycin in this case emphasize the need for additional research regarding risk factors for acquisition of VRSA.