Variation in methicillin-resistant Staphylococcus aureus occurrence by geographic location and hospital characteristics.

A survey of 162 Veterans Administration Medical Center (VAMC) laboratories performing antimicrobial susceptibility testing was performed to determine variation in reported rates of methicillin-resistant Staphylococcus aureus (MRSA) isolation by geographic location and hospital characteristics. Of the 162 VAMC laboratories surveyed, 136 (84%) provided usable data. The percentage of S aureus isolates reported as resistant to methicillin ranged from 0% to 52% with a mean value of 10% among the 136 survey respondents. MRSA were isolated in every VA Medical District and 96% of all respondent laboratories reported isolating at least one MRSA isolate during the preceding year. These data are considered an underestimate of the time MRSA rate in the VA system due to the fact that many laboratories failed to follow key methodologic guidelines for optimal detection of MRSA. A positive correlation was found between MRSA isolation rate and several measures of hospital size and activity including total beds, total admissions, and total antimicrobial susceptibility tests performed. Geographic clustering of MRSA isolation was observed with distinct areas of very high and very low percentages of S aureus isolates reported as MRSA. The data suggest that the geographic distribution of MRSA within the VA system should be monitored closely for evidence of spread from areas with high-MRSA rates to areas of mid- or low-MRSA rates. Evidence of increased MRSA isolation within these areas may necessitate increased caution in patient referral and transfer patterns within the VA system.