
A study of positive blood cultures over a 5-year period found that antimicrobial resistance (AMR) was associated with a 10% relative increase in the risk of death among patients with bacteremia, Canadian researchers reported today in Clinical Infectious Diseases.
Using linked microbiologic data from 114 hospital, community, and public health laboratories in Ontario, a team led by researchers from the University of Toronto and Public Health Ontario developed a cohort of patients with positive blood cultures from 2017 through 2021. They focused their analysis on pathogens responsible for at least 150 bloodstream infections and at least 20 associated deaths, and selected antibiotics for which susceptibility results were reported in at least 10% of episodes, with a resistance proportion from 1% to 99%. The primary outcome was 30-day mortality.
A total of 83,962 bacteremia episodes caused by 30 pathogens were identified, with 11 eligible pathogen-antibiotic combinations. Overall 30-day mortality was 17.1%. The most common pathogens were Escherichia coli (30.8%), Staphylococcus aureus (17.6%), and Klebsiella spp. (10.0%). The average patient age was 70 years, and 54.9% were male.
Larger impact for commonly used antibiotics
Across the 110 pathogen-antibiotic combinations studied, any resistance was associated with a 47% increased risk of 30-day mortality (hazard ratio [HR], 1.47; 95% confidence interval [CI], 1.32 to 1.65) in unadjusted analyses. But after adjusting for age, sex, healthcare exposures, comorbidities, and co-resistance, the increased risk of 30-day mortality was 10% (HR, 1.10; 95% CI, 1.07 to 1.16). The risk was 18% higher for resistance to antibiotics commonly used for empiric treatment (HR, 1.18; 95% CI, 1.10 to 1.26).
Attributable mortality due to AMR over the study period was 896 deaths, or 1.2 per 100,000 population per year.
"These results suggest that treatment adequacy could be an important mechanism leading to AMR-associated mortality, and that the mortality burden will increase if resistance rates to our most common treatment agents increase," the study authors wrote. "Ongoing surveillance and global collaboration is needed to better document and limit the impacts of antimicrobial resistance."