Strengths and limitations
This study has several major strengths. First, we used catheterized urine specimens instead of voided urine. Indeed, Wolfe and coworkers discovered that the microbiomes in voided urine and urine collected by transurethral catheter differed, and microbiome in catheterized urine specimens most closely represent the bladder microbiome itself, without contribution of microbial flora from the genital tract.12 Second, except the scores of OABSS, the demographic characteristics (e.g., age, BMI, race/ethnicity) of the two cohorts were similar. Therefore, many factors that cause the heterogeneity of flora are excluded. Third, the total sample size of well-characterised OAB patients included in this study is relatively large. In addition, all patients not only completed the routine urine examination, but also underwent standard urine culture to rule out urinary tract infection. The limitations of the study include small sample size of mild OAB group and lack of a replication dataset. And it is hardly to determine the cause-effect relationship between symptoms and bioinformatics indicators in this cross-sectional study. Thus, prospective studies with a larger sample will be required to clarify the role of urinary microbiota in the development and progression of OAB.