Incidence and factors associated with rapid blood culture sterilization among patients receiving ertapenem combination therapy for MSSA bacteremia

Ertapenem combination therapy has been shown to expedite the time to blood culture sterilization among patients with MSSA bacteremia. The purpose of this study was to define what proportion of patients sterilizes blood cultures within 72 h of ertapenem combination treatment initiation. This was a retrospective, multicenter study of patients who received ertapenem combination therapy for MSSA bacteremia. Patients were considered to have rapid blood culture sterilization if blood cultures were negative within 72 h of ertapenem initiation and delayed blood culture sterilization if blood cultures remained positive after 72 h of ertapenem initiation. Of the 304 patients with MSSA bacteremia who received ertapenem for combination treatment, 197 met the inclusion criteria. The median (IQR) time to ertapenem initiation from the time of blood culture obtainment was 4 (3-5) days, and 47% (93/197) had definitive endocarditis. Overall, 85% (167/197) had rapid blood culture sterilization. Patients who had delayed blood culture sterilization had a trend toward a higher Pitt Bacteremia Score at the time of blood culture obtainment (2 [0-4] vs 1 [0-2], <i>P</i> = 0.091) and were more likely to have an oxacillin minimum inhibitory concentration of ≥0.5 µg/mL (67% vs 43%, <i>P</i> = 0.015) compared to those with rapid blood culture sterilization. In this large study of patients who received ertapenem combination therapy for MSSA bacteremia, 85% of patients sterilized their blood cultures within 72 h of treatment. These results suggest that a standard 3-day ertapenem course could be a reasonable stewardship strategy for patients initiated on combination therapy for MSSA bacteremia.