Research Article: What can we learn by examining variations in the use of urine culture in the management of acute cystitis? A retrospective cohort study with linked administrative data in British Columbia, Canada, 2005-2011

Date Published: March 8, 2019

Publisher: Public Library of Science

Author(s): Rachel McKay, Michael Law, Kimberlyn McGrail, Robert Balshaw, Romina Reyes, David M. Patrick, Dafna Yahav.


Urinary tract infections (UTI) are common community-based bacterial infections. Empiric antibiotic recommendations are guided by local resistance rates. Previous research suggests that cultures are overused for uncomplicated cystitis, but practice patterns have not been described in detail. Variations in culturing have implications for the interpretation of antibiotic resistance rates.

We used a retrospective cohort study to analyze variations in urine culturing among physicians, controlling for patient and physician characteristics. We identified all outpatient physician visits among adults and children for cystitis in British Columbia between 2005 and 2011 using administrative data and linked these to laboratory data on urine cultures. Using hierarchical generalized linear mixed models we explored variations in urine culture submissions for cystitis (ICD code 595) and the associations with patient and physician characteristics, stratified by patient sex.

Urine cultures were associated with 16% of visits for cystitis among females and 9% among males, and 59% of visits overall were associated with antibiotic treatment. Older patients, patients with a recent antibiotic prescription, and long term care residents were significantly less likely to have a culture associated with a cystitis visit, whether male or female. Female physicians and physicians with 16–35 years’ experience were more likely to culture, while international medical graduates were less likely–particularly for female visits. Notably, there was substantial unexplained variation among physicians after controlling for physician characteristics: we found a 24-fold variation in the odds of culturing a female UTI between physicians who were otherwise similar.

Individual physicians show substantial variation in their propensity to submit cultures for cystitis visits. Reducing such variation and encouraging appropriate levels of culturing would support effective antibiotic use.

Partial Text

Urinary tract infections (UTI) affect approximately 10% of women over the age of 18 every year, and about 60% of women will experience at least one episode in her lifetime [1,2], making UTIs one of the most common types of bacterial infections among outpatients [3]. While more common in women, UTIs affect men as well. UTIs cause considerable discomfort and impact on quality of life [4–6], cost the healthcare system a significant amount (an estimated $2.3 billion in the US in 2010-equivalent dollars) [2,7], and add to the burden of antibiotic exposure which increases individual risk for antibiotic resistant infections as well as population-level spread of resistant bacteria [8].

We undertook a retrospective cohort study using linked administrative data.

During the study period, there were 1,288,696 visits for cystitis, by 595,714 unique patients, seen by 5,825 unique physicians. Male physicians conducted 71% of all visits; two-thirds of visits were conducted by Canadian medical school graduates; just over a quarter (26.1%) of visits were conducted by physicians with 0–15 years of experience, and almost half were conducted by physicians with 16–30 years of experience. Eighty-four percent of these visits were among female patients. Among females, more visits occurred among younger adults, with 56% of female visits occurring among patients between the ages of 15 and 54. In contrast, only 32% of male visits were in this age group. Fifty-nine percent of male visits were among those aged 55 or older, whereas 38% of female visits were. Overall, 58% of cystitis visits were associated with antibiotic prescription (22% with a prescription for ciprofloxacin, 17% with nitrofurantoin, 12% with trimethoprim/sulfamethoxazole) and.15% of visits were associated with a urine culture (Table 1).

Rising antibiotic resistance among uropathogens complicates the treatment of urinary tract infections. Culturing a UTI specimen can facilitate treatment through identification of the organism and susceptibility profile; however, given the stability of organism distribution and relative predictability of susceptibility probabilities, there is good evidence that there is no clinical advantage from routinely sending urine cultures from suspected uncomplicated cystitis for testing [30]. Microbiology services support optimal clinical care when used appropriately, and are an essential component of antimicrobial stewardship [31]. Overuse of culturing in uncomplicated UTI may represent potential system waste. However, in complicated cases, where the distribution of organisms and resistance patterns is less predictable, a urine culture can be important–both in terms of targeting the clinical management of the patient with the goal of reducing symptoms quickly, and for minimizing undue selection pressure for antibiotic resistance. Therefore, encouraging the appropriate balance of use is both a patient care and health system issue. This study found large variations between physicians in their propensity to culture, and these variations were larger than the marginal effect of any of our observed characteristics of patients or physicians.

This analysis suggests that physicians have highly variable tendencies to culture for cystitis, and the appropriate and efficient use of urine cultures can likely be improved. Further research is necessary to confirm these exploratory findings. However, effort directed towards both promoting the use of urine cultures in relevant cases, and restricting their use when not required, would not be misplaced. This effort could involve targeted audit and feedback to primary care providers and alignment with Choosing Wisely initiatives.




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