Antibiotic Administration Before Bacterial Culture Collection Reduces Positivity Rate within Minutes: A Multicenter Cohort Study

Background: Prompt antibiotic administration improves outcomes, but antibiotic administration prior to culture collection cultures can decrease culture yield. We sought to determine impact of antibiotic administration timing on the positivity rate of blood, urine, and respiratory cultures. Methods: Over three years we conducted a multicenter retrospective cohort study of adult inpatients with blood, urine or respiratory cultures collected who received at least one antibiotic. The first specimen of each culture type was included. The primary outcomes were rates of positive cultures and time of collection relative to first antibiotic administration. Findings: Of 34,677 patients with at least one blood, urine or respiratory culture collected in addition to at least one antibiotic dose administered during the study period, 14,909 cultures (7,351 sets of blood, 7,081 urine, and 477 respiratory cultures) were eligible for analysis. Most (79%) cultures were collected before antibiotic initiation. During the first hour following antibiotic initiation, blood culture positivity decreased by 18% for every 15 minutes (odds ratio [OR]: 0·82, 95% confidence interval [CI]: 0·71-0·95), urine culture positivity decreased by 19% for every 15 minutes (OR: 0·81 [95% CI: 0·76-0·86]) there was no significant change in respiratory culture positivity. Interpretation: Antibiotic administration significantly and promptly decreases yield of blood and urine bacterial cultures. Funding Statement: JTJ was partly supported by the CDC Prevention Epicenters (U01CK00054). Declaration of Interests: The authors have no conflict of interest. Ethics Approval Statement: The study was reviewed and considered exempt by the Emory University’s Institutional Review Board.