Treatment outcomes with cefazolin versus oxacillin for deep-seated methicillin-susceptible Staphylococcus aureus bloodstream infections.

Clinical preference for a semisynthetic penicillin (oxacillin or nafcillin) over cefazolin for deep-seated methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infections (BSI) perseveres despite limited data to support this approach. A retrospective cohort study of patients treated for MSSA BSI with either oxacillin or cefazolin was performed across two medical centers in Chicago, IL. The outcome measures included documented in-hospital treatment failure, all-cause in-hospital mortality, duration of MSSA BSI, and incidence of documented adverse events. Of 161 patients with MSSA BSI, 103 (64%) received cefazolin, and 58 (36%) received oxacillin. The identified sources of BSI were central line (37.9%), osteoarticular (18%), and skin and soft tissue (17.4%). Patients with endocarditis (29/52 [44.2%]) and other deep-seated infections (23/52 [55.8%]) were classified under the subset of deep-seated infections (52/161 [32.3%]). Multivariate models found deep-seated infection (adjusted odds ratio [aOR], 4.52; 95% confidence interval [CI], 1.23 to 16.6; P = 0.023), metastatic disease (aOR, 4.21; 95% CI, 1.13 to 15.7; P = 0.033), and intensive care unit (ICU) onset of infection (aOR, 4.80; 95% CI, 1.26 to 18.4; P = 0.022) to be independent risk factors for in-hospital treatment failure. Treatment group was not an independent predictor of failure (aOR, 3.76; 95% CI, 0.98 to 14.4; P = 0.053). The rates of treatment failure were similar among cefazolin-treated (5/32 [15.6%]) and oxacillin-treated (4/20 [20.0%]) patients (P = 0.72) in the subset of deep-seated infections. Mortality was observed in 1 (1%) and 3 (5.2%) cases of cefazolin- and oxacillin-treated patients, respectively (P = 0.13). Cefazolin was not associated with higher rates of treatment failure and appears to be an effective alternative to oxacillin for treatment of deep-seated MSSA BSI.