Background: The purpose of this study was to determine whether any indexes of vaginal microecology evaluation system (VMES) could predict sexually transmitted infections (STIs).Methods: A total of 1032 women, who presented to Gynecology Outpatient Clinic of the First Affiliated Hospital of Xi'an Jiaotong University between November 2016 and November 2020, were included in the study. Incident STIs was defined as any case of Chlamydia trachomatis (CT), Mycoplasma genitalium (MG) and Neisseria

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... rrhoeae (NG), and were confirmed using the RNA-based simultaneous amplification and testing (SAT) assay. VEMS is structured in two parts, one is the morphological characterizations encompassing bacterial density, flora diversity, predominant flora, pathogenic microorganisms and indicators of inflammation, the other is the functional indexes, including vaginal pH, cleanliness, hydrogen peroxide (H2O2), sialidase, β-glucuronidase, leukocyte esterase, and acetylglucosaminidase. Bacterial vaginosis (BV) was diagnosed by Gram stain (Nugent score). Associations were mainly assessed using logistic regression (LR).Results: SAT assay detected STIs in 64 (6.2%) of the 1032 samples tested and 136 (13.2%) women had a clinical BV diagnosis using Nugent score. Multivariate logistic regression analysis revealed that women with sialidase-positive were more likely to test positive for STIs (aOR=3.081, 95% CI=1.586-5.984, P=0.001). Of 896 women without clinical BV, significant association was also found for sialidase and STIs (aOR =4.133, 95% CI= 1.140-14.978, P=0.031).Conclusions: Sialidase may be a useful indicator to help clinicians identify these women who are at risk for STIs, especially in the absence of BV population.