PURPOSE: To assess whether vancomycin minimum inhibitory concentration (MIC) 
creeps among clinical isolates of methicillin-resistant Staphylococcus aureus 
(MRSA) in a regional hospital in China. Furthermore, to analyze the causes of 
vancomycin MIC creeps and the relationship between vancomycin MICs and the 
outcome among patients with MRSA infection.
MATERIALS AND METHODS: All clinical isolates of MRSA from 2006-2010 were 
retrieved and tested by the broth microdilution procedure to determine their 
vancomycin MIC. Meanwhile, related patient records were analyzed.
RESULTS: While all isolates were susceptive to vancomycin, the percentage of 
isolates with a vancomycin MIC = 1 mg/L increased significantly from 2006 
(37.0%) to 2010 (75.7%). Meanwhile, vancomycin usage density (DDDs/1000 
bed-days) had increased significantly from 2006-2010. Mean linear correlation 
analysis showed a statistically significant positive correlation (r = 0.905, P < 
0.05) between the consumption of vancomycin and the percentage of MRSA isolates 
with a vancomycin MIC = 1 mg/L. Clinical records revealed high vancomycin MIC 
was associated with a higher microbiologic failure rate in MRSA bloodstream 
infections.
CONCLUSIONS: The data demonstrated vancomycin MIC creep among clinical isolates 
in our hospital, and the MIC creep may be caused by the increasing usage of 
vancomycin. Furthermore, the analysis strongly suggested this shift of 
vancomycin MIC within the susceptible range may be associated with an increasing 
probability of treatment failure.