The urine-culturing cascade: variation in nursing home urine culturing and association with antibiotic use and Clostridiodes difficile infection

Background — Rates of antibiotic use vary widely across nursing homes and cannot be explained by resident characteristics. Inappropriate antibiotic prescribing for a presumed urinary tract infection is often initiated by inappropriate urine culturing. We examined nursing home urine culturing practices and their association with antibiotic use.

Methods — We conducted a longitudinal, multilevel, retrospective cohort study based on quarterly nursing home assessments between April 2014 and January 2017 in 591 nursing homes and covering over 90% of nursing home residents in Ontario, Canada. Nursing home urine culturing was measured as the proportion of residents with a urine culture in the prior 14 days. Outcomes included receipt of any systemic antibiotic and any urinary antibiotic (e.g. nitrofurantoin, trimethoprim/sulfonamides, ciprofloxacin) in the 30 days after the assessment, and Clostridiodes difficile infection in the 90 days after the assessment. Adjusted Poisson regression models accounted for 14 resident covariates.

Results — 131,218 residents in 591 nursing homes were included. 7.9% of resident assessments had a urine culture in the prior 14 days, and this proportion was highly variable across the 591 nursing homes (10th percentile=3.4%, 90th percentile=14.3%). Before and after adjusting for 14 resident characteristics, nursing home urine culturing predicted total antibiotic use (adjusted risk ratio per doubling of urine culturing [RR]=1.21, 95% confidence interval [CI]: 1.18-1.23), urinary antibiotic use (RR=1.33, 95% CI: 1.28-1.38), and C. difficile infection (incidence rate ratio=1.18, 95% CI: 1.07-1.31).

Conclusions — Nursing homes have highly divergent urine culturing rates, and this variability is associated with higher antibiotic use and rates of C. difficile infection.