Expanded Culture Techniques Identify Uropathogens in "Contaminated" Cultures

Treating asymptomatic bacteriuria (ASB) during pregnancy is recommended to reduce adverse pregnancy outcomes. Some urine cultures reported as contaminated may represent clinically significant bacteriuria. Enhanced culture techniques detect more microbes than standard urine cultures.

The objective of this study was to characterize discordance in results from 3 culture approaches in asymptomatic pregnant patients screened for bacteriuria whose samples were flagged as contaminated by the clinical laboratory.

This was a planned secondary analysis of a randomized controlled trial comparing clean-catch urine and Peezy device collection in asymptomatic pregnant patients. Paired urine samples were sent to the clinical laboratory and a translational researcher's laboratory. Clinical laboratory standard urine culture results (clinSUC) deemed "contaminated" were compared with those from the research laboratory's standard culture (resSUC; same conditions, all identified microbes reported) and expanded quantitative urine culture (EQUC; more urine, expanded growth conditions, longer incubation). Discordant results included cases where (1) the relative abundance of known uropathogens identified by resSUC or EQUC exceeded 50% or (2) the predominant pathogen differed from clinSUC.

Sixty-seven participants had contaminated cultures. For clinSUC versus resSUC, discordance was 14 of 67 (20.9%). For clinSUC versus EQUC, discordance was 11 of 67 (16.4%). There was no significant difference between discordance rates (P= 0.51). Only 3 of 67 participants with contaminated cultures had a second urine specimen collected during pregnancy.

In asymptomatic pregnant patients, expanded culture and reporting techniques identified uropathogens in 16-21% of urine specimens for which standard urine culture results were interpreted as contaminated.