Table 1. Prevalence of hVISA* and VSSA phenotypes based on the macromethod E test and the vancomycin MIC of standard E test.
| Vancomycin MIC† (µg/mL) | MRSA (N=138) | MSSA (N=91) | ||
|---|---|---|---|---|
| hVISA* (%) | VSSA (%) | hVISA* (%) | VSSA (%) | |
| 0.25 | 0 (-) | 0 (-) | 0 (-) | 1 (0.0) |
| 0.5 | 0 (-) | 7 (100.0) | 0 (-) | 0 (-) |
| 0.75 | 1 (14.3) | 6 (85.7) | 1 (16.7) | 5 (83.3) |
| 1 | 22 (42.3) | 30 (57.7) | 0 (-) | 45 (100.0) |
| 1.5 | 38 (61.3) | 24 (38.7) | 7 (18.9) | 30 (81.1) |
| 2 | 8 (88.9) | 1 (11.1) | 1 (50.0) | 1 (50.0) |
| 3 | 1 (100.0) | 0 (-) | 0 (-) | 0 (-) |
| Total | 70 (50.7) | 68 (49.3) | 9 (9.9) | 82 (90.1) |
hVISA prevalences according to the vancomycin MICs were significantly different in MRSA (P=0.0007) and MSSA (P=0.0149) isolates. Categorical variables were compared using the Chi-square test by 2×N table format.
*hVISA phenotype was identified by macromethod E test; †Vancomycin MICs were determined by standard E test.
Abbreviations: VSSA, vancomycin-susceptible S. aureus; hVISA, heterogeneous vancomycin-intermediate S. aureus; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus.