Prevalence of asymptomatic bacteriuria in inpatients at Trillium Health Partners with low urine culture colony counts

Abstract

Rationale & Objectives Most laboratories (including Trillium Health Partners (THP)) report urine cultures with colony counts >10 x 106 cfu/L. This threshold was derived from studies in young non-hospitalized women, which have limited applicability to hospitalized patients. Inpatients have an increased risk of asymptomatic bacteriuria (ASB) compared to outpatients, potentially leading to overtreatment. Our primary objective was to determine the prevalence of ASB in low colony count urine cultures (10-100 x 106 cfu/L). Our secondary objectives assessed characteristics of these cultures. Methodology A retrospective chart review of inpatients admitted to THP with urine cultures sent between April 1st 2017 to November 31st 2017 was conducted. Patients were classified as having a urinary tract infection based on modified National Healthcare Safety Network (NHSN) criteria. Charts containing no documentation of symptoms or cases where patients had an alternate source of infection were classified as ASB. To demonstrate a prevalence of ASB of >85%, a sample size of 196 inpatients was required. A prevalence of >85% was used by other institutions to implement interventions reducing prescribing for ASB. Results 95/122 (77.9%) of low urine culture colony counts represented ASB at our institution. Of these, 36 (29.5%) patients were on antibiotics for an alternate source of infection and 27 (22.1%) were prescribed antibiotics for ASB. Additionally, 7 patients (5.7%) had bacteremia secondary to a urinary source, of which 2 patients (1.6%) were asymptomatic. Finally, 10% (122/1216) of total urine cultures (any growth) sent from included wards were low growth. Conclusions Based on interim results, the prevalence of ASB for low urine culture colony counts at our institution was <85%. Additional data collection is required to meet sample size (N=196) in order to sufficiently power this outcome. A future intervention altering reporting of low growth urine cultures might reduce prescribing for ASB, and will be considered if our prevalence is >85%.