Where has vancomycin-heterogeneously resistant Staphylococcus aureus gone?

7 years have passed since a strain of Staphylococcus aureus heterogeneously resistant to vancomycin was first identified in a Japanese hospital in 1996.1 The strain was initially characterised as containing a small number of vancomycin-intermediately resistant subpopulations (vancomycin minimum inhibitory concentration [MIC], ≥8 mg/L), such as Mu50, at a frequency of 1 per 1 000 000. Warnings were sent out that such strains had already been disseminated in several Japanese medical institutions, despite the fact that they would hardly be detected by routine antimicrobial susceptibility testing recommended by the National Committee for Clinical Laboratory Standards, since only around 1000 colony forming units of bacterial cells undergo testing.