Raising Urinary Tract Infection Threshold Cuts Unnecessary Antibiotic Use, Without Harming Patients

Raising the laboratory threshold for identifying potential urinary tract infections (UTIs) may prevent unnecessary antibiotic treatment in nearly a third of asymptomatic bacteriuria and candiduria (ASB/C) cases among hospitalized patients, according to a research letter published April 29 in JAMA Internal Medicine.

Unnecessary antibiotic treatment for ASB/C is common among hospitalized patients, in part because the optimal colony-count threshold for reporting growth from inpatient urine cultures remains uncertain. Previous research suggests that low colony counts of organisms (104 to 105 colony-forming units [CFU]/mL) are infrequently associated with UTI but are associated with antimicrobial prescribing.

At Sunnybrook Health Sciences Centre the threshold for identifying potential uropathogens from urine cultures submitted from inpatient units was increased from 104 CFU/mL or greater to 105 CFU/mL or greater on March 1, 2017. Reports for urine cultures with low colony counts stated that these organisms usually represent ASB/C, but telephone consultation was available for any clinician with a high suspicion for UTI. Rates of antibiotic treatment for all patients with low-colony-count UC (the intervention group) and every second patient with a high-colony-count culture result (more than 105 CFU/mL; control group) were compared for the preintervention period (March 1, 2016, to Feb. 28, 2017) and the postintervention period (March 1, 2017, to Feb. 28, 2018) using chart review.

The researchers identified 609 patients with a low colony count, and 1,432 patients with a high colony count, of which 608 and 690, respectively, were included in analysis. Changing the threshold for identifying UTIs was associated with a significant and sustained reduction in antimicrobial prescribing for ASB/C in the low-colony-count group compared with the high-colony-count group, without evidence of undertreatment of UTI. When clinicians requested low-colony-count UCs to be worked up (n = 17), patients were significantly more likely to have a UTI. No significant differences in clinical outcomes were seen between the pre- and post-intervention groups.

“The simple change of raising the threshold for identifying potential urinary pathogens may avert nearly a third of ASB/C treatment among hospitalized patients and could have scalable impact on improving antimicrobial use in acute care hospitals,” write the authors led by Marc-Andre Smith, M.D., from University of Toronto.

Takeaway: Upping the laboratory threshold for UTI diagnosis may improve antibiotic stewardship among hospitalized patients.