Duration of Pre-Operative Antibiotic Treatment and Culture Results in Patients With Infective Endocarditis.

Background: Bacterial growth in cultures of resected heart valves of patients with infective endocarditis (IE) is influenced by pre-operative antibiotic treatment (preop-AT).

Objectives: This study sought to evaluate the time dependency of valve culture results (positive valve culture [PVC] vs. negative valve culture) on preop-AT.

Methods: A total of 352 IE episodes in 344 adult patients of our tertiary referral hospital were retrospectively investigated (2005 to 2016). The primary endpoint was PVC results. The study used a logistic additive model adjusted for bacterial species, the McCabe-Jackson classification, and the existence of foreign valve material as covariables.

Results: The 231 included IE cases (187 [81%] men, median age 62 years, 153 [66%] native valves) comprised 58 (25%) PVC results and 173 (75%) negative valve culture results. A multivariable analysis adjusted for bacterial species, McCabe-Jackson classification, and valve type resulted in odds ratios for PVC of 6.35 (95% confidence interval [CI]: 1.94 to 20.78; p = 0.002) and 3.93 (95% CI: 1.57 to 9.84; p = 0.003) for Enterococcus spp. and Staphylococcus spp., respectively. Model-based odds ratios for PVC risk reduction in 2-day intervals of preop-AT ranged from 0.64 (95% CI: 0.61 to 0.68) at day 7 to 0.74 (95% CI: 0.70 to 0.78) at day 13 and 0.98 (95% CI: 0.93 to 1.02) at day 21.

Conclusions: In IE cases treated with valve surgery, Staphylococcus aureus and Enterococcus spp. were associated with valve culture growth. After 7 days of antibiotic treatment, the additional effect of preop-AT on valve culture results per 2-day interval was minor. Antibiotic treatment beyond 21 days had no influence on culture results.