Association Between Erythromycin or Clindamycin Resistance and 30-Day Mortality in Patients With MSSA Bacteremia

<b>Objectives:</b> The objective of the present study is to assess the association of erythromycin and clindamycin susceptibilities with 30-day mortality in patients with MSSA bacteremia treated with cefazolin. <b>Methods:</b> Retrospective cohort study of patients with least one positive blood culture growing MSSA and treated with cefazolin for at least 3 consecutive days. Groups included patients who had an MSSA strain that was both erythromycin and clindamycin susceptible (E/C-S), the comparator group included patients with erythromycin resistant and clindamycin resistant or susceptible (E/C-R) MSSA strains. The relative risk for 30-day mortality was calculated for E/C-R compared to E/C-S along with the sensitivity and specificity for E/C-R as a predictor of 30-day mortality. <b>Results:</b> A total of 114 patients were eligible for analysis; with 72 (63%) categorized in the E/C-S group and 42 (37%) categorized in the E/C-R group. The primary outcome of 30-day mortality was met in 7 (10%) patients in the E/C-S group vs 7 (17%) in the E/C-R group; unadjusted relative risk (95% CI) 1.71 (0.65-4.55). The sensitivity and specificity of E/C-R as a predictor of 30-day mortality was 50% (95% CI = 23-77) and 65% (95% CI = 55-74), respectively. <b>Conclusions:</b> This exploratory study did not find clindamycin or erythromycin susceptibility to be associated with 30-day mortality in patients treated with cefazolin for MSSA bacteremia. The relevance of this surrogate marker in clinical practice is negligible due to its limitations, and future investigations are required to establish pragmatic means of detecting isolates which may be insufficiently treated with cefazolin.