Approximately three quarters of all invasive methicillin‐resistant Staphylococcus aureus (MRSA) infections in the United States are bloodstream infections (BSIs). Many patients with MRSA BSIs are not treated with effective definitive therapy even when antibiotic susceptibility results are known. Inappropriate antibiotic selection for MRSA BSIs results in poor clinical outcomes.


We performed a retrospective case–cohort study of consecutive patients with MRSA BSIs from 10 hospitals (1 tertiary‐care and 9 community medical centers) from 1999 to 2003. Patients were included if they were alive and remained at a study hospital on day 3 following a positive MRSA blood culture. Data were extracted by chart review. The primary end point was the administration of effective definitive therapy within the first 3 days following the first positive MRSA blood culture. Effective definitive therapy was defined as receipt of 1 or more of the following antimicrobial agents: daptomycin, linezolid, quinupristin/dalfopristin, or vanco‐mycin. Multivariable logistic regression was used to determine variables associated with receipt of effective definitive therapy.


Five hundred and sixty‐two patients were studied. Of these, 482 were alive and hospitalized on day 3. The mean age of the cohort was 63 years, and 50% were male. Three hundred and seventy‐four patients (77.6%) had received appropriate definitive therapy against MRSA by day 3. In multivariable analysis, patients were more likely to receive effective therapy if they were at a tertiary‐care center (OR, 1.96; 95% CI, 1.16–3.40), had a McCabe score of 1 (indicating an expected survival < 2 weeks; OR, 1.97; 95% CI, 1.11–3.71), or a central venous catheter at the time of admission (OR, 1.96; 95% CI, 1.14–3.739). Patients with a primary BSI at the time of admission (OR, 0.326; 95% CI, 0.183–0.56) were less likely to receive effective definitive therapy.


In our study, 108 patients with MRSA BSIs (22.4%) did not receive effective definitive therapy for MRSA by day 3 following the first positive blood culture. The presence of a primary BSI was associated with inappropriate definitive therapy for MRSA BSI, suggesting that providers underrecognized the infection risk of catheters placed after admission to the hospital. Treatment at a tertiary‐care center, high acuity of illness, and the presence of a central venous catheter at admission predicted higher rates of appropriate definitive therapy. Further studies to clarify the factors that contribute to inappropriate definitive therapy and evaluation of contemporary prescribing practices for patients with MRSA BSI are needed. In addition, our results suggest the need for provider notification, both when the blood culture is positive and when sensitivities are resulted.


C. Herzke ‐ none; L. Chen ‐ none; D. Brotman ‐ none; D. Anderson ‐ none; Y. Choi ‐ none; K. Kaye ‐ none