Addition of anaerobic coverage for treatment of biliary tract infections: a propensity score-matched cohort study.

Objectives: To evaluate whether additional antibiotics that target anaerobes, including Bacteroides spp., are associated with improved clinical outcomes in patients with biliary tract infections (BTIs). Methods: This was a retrospective propensity score-matched cohort of adults aged ≥18 years with BTIs, admitted to hospital between 1 April 2015 and 30 March 2021. Eligible patients treated with antibiotics that provided coverage of anaerobes were compared with those treated with comparable regimens without anaerobic coverage. The primary outcome was a composite of mortality within 30 days or relapse within 90 days of source control or completion of antibiotics. Secondary outcomes included length of stay (LOS), duration of antibiotic therapy and adverse drug reactions. ORs were calculated using a weighted generalized linear regression model with propensity-score matching. Results: Among 398 patients included, 209 were treated without anaerobic coverage and 189 with anaerobic coverage. After propensity-score matching, there was no significant difference in primary outcome between propensity-matched patients who received additional anaerobic coverage and those who did not [adjusted OR (aOR) 1.23; 95% CI 0.69-2.22)]. Those with anti-anaerobic coverage had longer LOS (aOR 4.85; 95% CI 1.68-13.98) and longer duration of antibiotic treatment (aOR 4.14; 95% CI 2.61-6.57) than those who did not receive additional anaerobic therapy, but not more adverse drug reactions (aOR 1.01; 95% CI 0.97-1.05). Conclusions: Omitting anti-anaerobic antibiotics may be a safe antimicrobial stewardship intervention. However, a randomized controlled trial may be warranted to definitively conclude whether additional anaerobic coverage in BTI treatment is necessary.