Does erythromycin/clindamycin resistance predict 30-day mortality in MSSA bacteremia?

Clindamycin or erythromycin susceptibility does not appear to contribute to 30-day mortality in patients with MSSA bacteremia treated with cefazolin, reports a study.

Overall, 114 patients with at least one positive blood culture growing MSSA and treated with cefazolin for at least 3 consecutive days were included in this retrospective cohort study. They were grouped into those with an MSSA strain that was both erythromycin and clindamycin susceptible (E/C-S) and those with erythromycin resistant and clindamycin resistant or susceptible (E/C-R) strains.

The investigators then calculated the relative risk (RR) for 30-day mortality, the primary outcome, for both groups, along with the sensitivity and specificity for E/C-R as a predictor of 30-day mortality.

Of the patients, 72 (63 percent) were included in the E/C-S group and 42 (37 percent) in the E/C-R group. Mortality within 30 days occurred in seven (10 percent) patients in the E/C-S group compared with seven (17 percent) in the E/C-R group (unadjusted RR, 1.71, 95 percent confidence interval [CI], 0.65‒4.55).

E/C-R as a predictor of 30-day mortality had a sensitivity of 50 percent (95 percent CI, 23‒77) and specificity of 65 percent (95 percent CI, 55‒74).

“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,” the investigators said.