Background: Vancomycin (VAN) is a mainstay of anti-staphylococcal therapy. Although the use of VAN to treat Staphylococcus aureus with VAN MIC ≥2 µg/mL may be associated with poor outcomes, the impact of VAN MIC in CoNS BSI is unknown. We examined the outcomes of three groups of patients with CoNS BSI: 1) treatment with VAN for an isolate with MIC ≥2 µg/mL; 2) treatment with an alternative agent for an isolate with MIC ≥2 µg/mL; and 3) treatment with VAN for an isolate with MIC <2 µg/mL.
Methods: We reviewed patients diagnosed with CoNS BSI between 2001 and 2016, treated with ≥7 days of parenteral VAN or an alternative (e.g., daptomycin, ceftaroline, linezolid). We only included monomicrobial infection and the first isolate where MIC was determined. Demographics, Charlson comorbidity index (CCI), source of infection, length of treatment (LOT), length of stay (LOS), treatment setting, and 90 day mortality were ascertained. Treatment failure was defined as infection relapse, hospitalization or surgery for infection within 90 days of therapy, and incomplete, extended or unplanned oral suppressive therapy.
Results: We identified 608 patients with CoNS blood isolates, 372 (61%) of which had MIC ≥ 2 µg/mL. The proportion of isolates with MIC ≥ 2 µg/mL decreased over time (67% in 2001-2011 vs. 35% in 2011-2016). Among 72 patients who met inclusion criteria, 44 (61%) had isolates with MIC ≥ 2 µg/mL and were treated with VAN (Group 1), 6 (9%) had isolates with MIC ≥ 2 µg/mL and received daptomycin (Group 2), and 22 (30%) had isolates with MIC <2 µg/mL and were treated with VAN (Group 3). Overall, the mean age was 64 years, 51% were black, CCI was 6, 62% had catheter-related BSI, LOT and LOS were 18 and 19 days, respectively. Mortality occurred in 8 (18%) patients in Group 1, 4 (66%) in Group 2, and 3 (14%) in Group 3. Treatment failure occurred in 11 (25%) patients in Group 1, 2 (33%) in Group 2, and 8 (36%) in Group 3. These differences did not reach statistical significance (p >0.05). Patients with isolates with MIC ≥ 2 µg/mL were less likely to require treatment in the acute care setting.
Conclusion: We did not detect a negative impact of VAN MIC ≥2 µg/mL on the outcome of patients who receive VAN for the treatment of CoNS BSI. Factors such as treatment setting and VAN levels may have influenced our results.