Impact of an Assay That Enables Rapid Determination of Staphylococcus Species and Their Drug Susceptibility on the Treatment of Patients with Positive Blood Culture Results

Abstract

Objective.To determine whether an earlier determination of staphylococcal species and their antibiotic susceptibility decreases unnecessary antistaphylococcal treatment and/or facilitates earlier appropriate treatment.Methods.We used the Xpert MRSA/SA BC system (Cepheid) for immediate determination of species and their drug susceptibility in patients whose blood cultures revealed gram-positive cocci in clusters. We compared the treatment of patients whose physicians received early notification of these results (group 1) with the treatment of patients in a historical cohort with delayed reporting after traditional microbiological studies (group 2). Outcomes were analyzed according to whether blood culture was positive forStaphylococcusspecies other thanS. aureus,methicillin-susceptibleS. aureus(MSSA), or methicillin-resistantS. aureus(MRSA) and whether the drugs used were appropriate for methicillin-susceptible or methicillin-resistant staphylococci (hereafter referred to as “MSS drug” or “MRS drug” therapy, respectively).Results.There were 44 (76%) of 58 patients with bacteremia due toStaphylococcusspecies other thanS. aureusin group 1 and 58 (55%) of 106 patients with bacteremia due toStaphylococcusspecies other thanS. aureusin group 2 who received no antistaphylococcal antibiotics (P<.01). Five (6%) of 89 patients in group 1 and 31 (25%) of 123 patients in group 2 received 0-168 hours (0-7 days) of MRS drug therapy (P< .01). Among patients with MSSA bacteremia, the mean time to initiation of appropriate therapy was 5.2 hours in group 1 and 49.8 hours in group 2 (P< = .007). Excluding patients who received MRS drug therapy for unrelated conditions, the mean duration of treatment was 19.7 hours in group 1 and 80.7 hours in group 2 (P= .003). Six (50%) of the 12 patients in group 1 and 39 (81%) of the 48 patients in group 2 received MRS drug therapy for MSSA bacteremia (P= .025). Time to initiation of therapy for MRSA bacteremia did not differ between groups.Conclusions.The use of an assay with rapid results reduced the use of antistaphylococcal therapy among patients who did not haveS. aureusbacteremia; it also decreased the use of MRS drug therapy and led to earlier appropriate therapy among patients with MSSA bacteremia.