Rate of Urine Culture Contamination with Different Methods of Urine Specimen Collection.

Abstract

Background: Midstream urine (MSU) samples are commonly collected at the time of patient evaluation despite known high rates of contamination.

Objective: The primary objective of this study was to evaluate the rate of mixed flora results in urine specimens obtained by MSU compared to straight catheterization urine (SCU).

Study design: This was a quality improvement project evaluating urine culture results of women who provided either an MSU or SCU sample for analysis. Adult women seen within urogynecology clinics at a tertiary care center between April and August 2023 who had urine cultures performed for any indication were included. Mixed flora was defined as the presence of ≥ 2 non-uropathogens or 1 uropathogen in low quantity (at least 10 times fewer) compared to the concentration of nonsignificant organisms.

Results: Three hundred forty women provided a urine specimen during the study period. SCU collection was performed for 171 (50.3%) women while 169 (49.7%) provided an MSU sample. Overall, 18.8% of urine cultures were reported as mixed flora (33.1% in MSU and 4.7% in SCU, p < 0.001). Mixed flora was more common with MSU specimens (87.5%, p < 0.001) and associated with a higher BMI compared to positive or negative cultures (mixed flora 29.8 kg/m² ± 16.3, positive or negative cultures 27.8 kg/m² ± 7.0, p = 0.04). MSU samples had increased odds of urine contamination compared to SCU collection (7.40 aOR, 95% CI 3.01-18.24).

Conclusion: The prevalence of mixed flora was reduced significantly when SCU samples were obtained. Clinicians should consider performing SCU collection when a urine specimen is required for patient evaluation.