The Safety and Impact of Raising the Urine Culture Reporting Threshold in Hospitalized Patients

Objective: To assess the impact of changing the reporting threshold policy of positive urine cultures in hospitalized non-pregnant adults from 10⁴ CFU/mL to 10⁵ CFU/mL on the unwarranted use of antibiotics and patient safety. Setting: A 1100-bed tertiary-care hospital in southern Israel. Methods: As an intervention, we changed urine culture reporting policy for patients admitted to general medical wards. If culture grew ≥10⁵ CFU/mL, it was reported with pathogen and antibiotic susceptibility data, if it grew ≤10⁴ CFU/mL, it was reported as “low growth". The withheld information was available upon request. We retrospectively collected data on all patients in a four-month period following the intervention and report using STROBE guidelines. Results: 7808 patients were admitted, in whom 3523 urine cultures were obtained. A total of 496 grew a pathogen, 51 were excluded (candida spp. positive, history of urinary surgery, obtained from catheter). A total of 300 were reported as positive and 145 were reported as low-growth. A higher rate of patients in the low-growth group were not treated with antibiotics 45/145(31%) vs. 56/300(18.7%) in the positive group p = 0.015 and the antibiotic duration of treatment was shorter by day 5 (IQR 0.9) vs. 6 (IQR 0.9) p = 0.015. No between-group difference was observed in recurrent admission rates, pyelonephritis within 30 days, bacteremia or all-cause mortality. Conclusions: Changing the reporting threshold of positive urine culture results from 10⁴ CFU/mL to 10⁵ CFU/mL in hospitalized patients reduced the number of patients who were unnecessarily treated for asymptomatic bacteriuria without negatively impacting patient safety. We urge microbiological laboratories to consider this change in threshold as part of an antimicrobial stewardship program.