Long-term risk of infection among patients colonized with antimicrobial-resistant pathogens: a population-wide cohort study

Background — Antimicrobial-resistant (AMR) pathogens represent an ongoing global health burden. Colonization is often a prerequisite for infection, but the risk of infection after AMR colonization is not well understood. Using population-level health administrative data, we sought to investigate the risk of infection with the same AMR organism after detection of colonization.

Methods — We conducted a retrospective population-wide cohort study among residents of Ontario, Canada, over a 5-year period to determine the risk of infection after detection of colonization with the following AMR pathogens: methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, extended-spectrum β-lactamase–producing Enterobacterales, and carbapenemase-producing Enterobacterales. We also examined the effects of age, sex, and health care setting of colonization detection on subsequent infection risk.

Results — There were 69 998 individuals with a positive AMR pathogen surveillance test result during the study period, 15.6% of which subsequently developed a sterile or nonsterile site infection within a median 57 days (IQR, 11–228). Infection rates varied among organisms: 18.3% for methicillin-resistant S aureus within a median 57 days (IQR, 10–239), 2.8% for vancomycin-resistant Enterococcus within a median 37 days (IQR, 11–119), 21.5% for extended-spectrum β-lactamase–producing Enterobacterales within a median 71 days (IQR, 18–231), and 20.3% for carbapenemase-producing Enterobacterales within a median 10 days (IQR, 3–42). A positive surveillance test result detected in a hospital was associated with increased infection risk after colonization as compared with the community setting.

Conclusions — The overall infection rate after colonization with an AMR pathogen was high for most organisms, highlighting the importance of detecting colonization from both an infection control and empiric antibiotic selection perspective.