To synthesize evidence on institutional spillover effects of antimicrobial use (AMU) on antimicrobial resistance (AMR) and Clostridioides difficile infections on individuals without direct antimicrobial exposure.

Systematic review.

Three databases were searched through August 2024 for studies evaluating spillover effects of AMU on unexposed individuals in institutional settings. Study characteristics, AMU, and outcomes were extracted. Study quality was assessed based on underlying methodology to detect spillover effect. A hybrid synthesis, including effect direction and meta-analysis of studies reporting continuous AMU and non-aggregate outcomes was utilized. Reporting followed PRISMA guidelines.

Of 5916 screened studies, five observational studies met inclusion criteria. Three were conducted across 68 hospital wards (ward-level exposure), and two across 693 nursing homes (facility-level exposure). Three studies evaluated all antimicrobial classes; two focused on penicillins, fluoroquinolones, and carbapenems. Two studies examined C. difficile, one MRSA, one carbapenem-resistant Enterobacterales, and one reported combined AMR and C. difficile outcomes. Low to moderate quality evidence indicated a positive spillover effect direction with increasing facility AMU. Meta-analysis of three studies yielded a pooled IRR of 1.54 (95% CI 0.85–2.80) per 100 days of therapy per 1,000 patient-days, with significant heterogeneity (I2 = 97.6%).

This review identified five studies suggesting a positive association between institutional AMU and collateral risks of AMR and C. difficile among unexposed individuals. Findings were limited by methodological heterogeneity and potential publication bias. Standardizing terminology, specifying spillover mechanisms, and adopting robust observational designs can enhance future research on spillover effects.

The relationship between hospital antibiotic use and antibiotic resistance is poorly understood. We evaluated the association between antibiotic utilization and resistance in academic and community hospitals in Ontario, Canada.

We conducted a multicenter observational ecological study of 37 hospitals in 2014. Hospital antibiotic purchasing data were used as an indicator of antibiotic use, whereas antibiotic resistance data were extracted from hospital indexes of resistance. Multivariate regression was performed, with antibiotic susceptibility as the primary outcome, antibiotic consumption as the main predictor, and additional covariates of interest (ie, hospital type, laboratory standards, and patient days).

With resistance data representing more than 90,000 isolates, we found the increased antibiotic consumption in defined daily doses per 1,000 patient days (DDDs/1,000 PD) was associated with decreased antibiotic susceptibility for Pseudomonas aeruginosa (−0.162% per DDD/1,000 PD; P=.119). However, increased antibiotic consumption predicted increased antibiotic susceptibility significantly for Escherichia coli (0.173% per DDD/1,000 PD; P=.005), Klebsiella spp (0.124% per DDD/1,000 PD; P=.004), Enterobacter spp (0.194% per DDD/1,000 PD; P=.003), and Enterococcus spp (0.309% per DDD/1,000 PD; P=.001), and nonsignificantly for Staphylococcus aureus (0.012% per DDD/1,000 PD; P=.878). Hospital type (P=.797) and laboratory standard (P=.394) did not significantly predict antibiotic susceptibility, while increased hospital patient days generally predicted increased organism susceptibility (0.728% per 10,000 PD; P<.001).

We found that hospital-specific antibiotic usage was generally associated with increased, rather than decreased hospital antibiotic susceptibility. These findings may be explained by community origins for many hospital-diagnosed infections and practitioners choosing agents based on local antibiotic resistance patterns.

Infect Control Hosp Epidemiol 2017;38:1457–1463