Staphylococcus aureus bacteremia in a secondary level Spanish hospital: clinical implications of high vancomycin MIC

One of the most controversial issues in recent years has been the clinical significance of high vancomycin MIC in Staphylococcus aureus bacteremia. The aim of this study was to elucidate the clinical implication that this parameter has in the staphylococcal bacteremia of a second level hospital.

Retrospective descriptive study between January 2014 and September 2016 with 138 records from the blood culture Severo Ochoa University Hospital registry. A total of 98 cases were finally analized. Microbiological analysis of vancomycin MIC was performed using micro dilution technique.

The mean age was 71.4 ± 12.45 and 63.26% of the patients had a Charlson index ≥6. A 30.61% were carriers of a venous central catheter. The most frequent source was venous central catheter (26.53%). There were 14.24% metastatic events. Global mortality rate at 30 days was 25.51%. The 43.87% of strains had a vancomycin MIC ≥ 2 mg/L. High vancomycin MIC was significantly associated with persistent bacteremia (OR 3.12 [1.13-8.93]), maintaining this statistical significance in methicillin-resistant S. aureus (MRSA) group (p =0.001) but no in methicillin-susceptible S. aureus (MSSA) group (p = 0.13). Persistent bacteremia was also significantly related with permanent catheter carriers (OR 4.18 [1.38-12.61]), peripheric catheter source (OR 5.18 [1.13-8.93]) and metastatic complications (OR 3.82 [1.03- 12.81]). There was no significant association between high vancomycin MIC and mortality.

High vancomycin MIC may be useful in daily clinical practice as a marker of poor clearance of S. aureus bacteremia, specially when is due to MRSA strains.