By Carol A. Kemper, MD, FACP

Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center

Dr. Kemper reports no financial relationships relevant to this field of study.

SOURCE: Brown KA, Daneman N, Schwartz KL, et al. The urine-culturing cascade: Variation in nursing home urine culturing and association with antibiotic use and C. difficile infection. Clin Infect Dis 2019. doi: 10.1093/cid/ciz482. [Epub ahead of print].

Inappropriate antibiotics use in nursing homes across North America continues driving antibacterial resistance and the risk of Clostridioides difficile infection (CDI) in the elderly. In my experience, one of the greatest offenses is the misinterpretation of urinalysis and culture results (a problem also common to the clinic and the acute care setting). Brown et al conducted a retrospective review of nursing home residents in Ontario, Canada, from 2014 to 2017. An assessment of nursing home residents was made once quarterly, documenting the proportion with a urine culture within 14 days of the assessment, the receipt of antibiotics within 30 days, and the incidence of CDI within 90 days. The researchers examined specific antibiotic use and noted those antibiotics commonly used for urinary tract infection (UTI), including ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole (TMP-SMX). Considering the national healthcare system, information about diagnosis and antibiotic use was available for about 91% of all nursing home residents in the province. CDI was based on both a diagnosis and the use of medication prescribed for CDI.

The analysis included 131,218 residents from 591 nursing homes. Of these, 71% were women, and 55% were > 85 years of age. Of these, 7.9% had a urine culture obtained within 14 days of the quarterly assessment (ranging from 3.4% for the lowest 10th percentile of facilities and up to 14.3% for the 90th percentile). Seventeen percent of residents received an antibiotic within 30 days, and 5.4% received an antibiotic commonly used for UTI. Antibiotic use within 30 days of assessment included, in decreasing order, ciprofloxacin (2.7%), cephalexin (2.6%), TMP-SMX (2.5%), nitrofurantoin (2.2%), Augmentin (2.1%), and other fluoroquinolones combined (2.6%). Urine culturing strongly predicted an increased use of antibiotics and explained 40% of the variability in antibiotic use between facilities, especially the use of nitrofurantoin. With every doubling of urine culturing, there was a 1.22-fold increase in total antibiotic use and a 1.36-fold increase in the use of antibiotics for UTI. CDI was diagnosed in 2,181 residents within 90 days. After adjusting for various factors, the rate of urine culturing at a facility was associated with a risk of CDI (for every doubling of culturing, the IRR for CDI was 1.18). Within 30 days of the quarterly assessment, 2.6% of residents died. Urine culturing was associated weakly with mortality.

These data suggest that different nursing homes have “a culture” of culturing urine, which drives the use of antibiotics at that facility. It is amazing to me that 17% of nursing home residents received an antibiotic every three months. The use of interventions and education to ensure appropriate collection of urine specimens and the interpretation of those results would go a long way to reducing inappropriate antibiotic use in nursing homes. For one thing, I always maintain that obtaining a clean catch in an elderly person is virtually impossible. Imagine you are older than 85 years of age, balancing yourself while holding your labia open with one hand, cleaning yourself with the other hand, and then catching the midstream urine without toppling over. My guess is that most of these specimens represent simple contamination. Furthermore, asymptomatic bacteriuria in elderly patients is not uncommon and does not require treatment.