Q Vancomycin-indeterminate S. aureus (VISA) has recently been reported in the United States. Which one of the statements concerning VISA is the most correct?
A. Minimum inhibitory concentration (MIC) for vancomycin is at least 1.0 mcg/mL
B. VISA isolates are usually methicillin susceptible (methicillin-resistant S. aureus, MRSA)
C. VISAs have emerged because of the extended use of vancomycin for MRSAs
D. VISA isolates are infrequent, so surveillance at the present time is not warranted Explanation The answer is c. (MMWR September 5, 1997, vol 46 No 35 pp 813–
815.) Vancomycin-indeterminate Staphylococcus aureus (VISA) were first recognized in Japan. Emergence in the United States soon followed. It is likely that the human VISA isolates have resulted from increased use of vancomycin for patients with MRSA or perhaps an increased pool of VISA in the environment selected out by the use of glycopeptides such as avoparcin, a growth promoter used in food producing animals. In patients with VISA, the Centers for Disease Control (CDC) strongly recommends compliance with isolation procedures and other infection control practices geared to control of VISA.