Using electronic health records to assess the relationship between colonization pressure and nosocomial pathogen acquisition.

Hospitalized patients are at risk for developing hospital acquired infections. Active surveillance for bacterial colonization is effective at preventing infection but is resource-intensive and limited to high-risk units and a subset of high-risk pathogens. Colonization pressure, defined as the prevalence of an organism among ward co-occupants, has been associated with hospital acquired infection and can be calculated in real-time using data in the electronic health record, but its use by infection control programs has been limited. As a proof-of-concept study, we built an open source informatics tool to model the impact of colonization pressure on nosocomial acquisition for a wide range of drug susceptible and resistant pathogens using electronic health record data from a large integrated health system in the Northeast United States, collected between May 2015 and July 2024. Using a matched case-control design, we show a consistent positive association between colonization pressure for an organism and nosocomial acquisition of that organism, regardless of whether that organism was drug susceptible or resistant. We also observed significant positive relationships between disparate organisms (e.g., colonization pressure from vancomycin resistant Enterococcus faecium and hospital acquisition of extended-spectrum beta-lactamase producing Klebsiella pneumoniae) as well as negative associations, primarily between organisms that inhabit distinct niches, such as colonization pressure from drug resistant Pseudomonas aeruginosa and hospital acquisition of vancomycin susceptible Enterococcus faecalis. Our results suggest nosocomial transmission of potential pathogens is widespread in a tertiary care hospital system with advanced infection control programs. We have made the software and our patient-level dataset publicly available to support future research and infection control interventions.