Geographic Variation in Diagnostic Performance of Amsel Criteria and Nugent Score for Vaginal Dysbiosis Defined by 16S rRNA Gene Sequencing

Background : Vaginal dysbiosis characterized by low abundance of vaginal lactobacilli and increased bacterial community diversity, is implicated in multiple adverse health outcomes and is an emerging target for preventive interventions, including live biotherapeutic products. The most common clinical presentation of vaginal dysbiosis is bacterial vaginosis (BV), but at least half of people are asymptomatic. Methods : We compared identification of BV by Nugent score and Amsel criteria for screening specimens from a Phase 1b randomized trial of a live biotherapeutic product conducted at 2 sites (CAPRISA, South Africa; MGH, USA), as well as a single follow-up visit from enrolled participants. Using 16S rRNA gene sequencing-based categorization of community state type (CST) as the reference and multinomial mixed-effects logistic models, we evaluated the association of Amsel BV and Nugent BV with CST IV (including subtypes IV-A and IV-B) and tested for site-specific effects. Results : Amsel BV was significantly associated with CST IV-A and IV-B; however, the strength of association was significantly diminished at CAPRISA compared with MGH, pointing to site-specific assessment differences or underlying biological variation. Nugent BV yielded stronger associations with CST IV-A, and IV-B and showed no evidence of a site-specific interaction, indicating consistent performance across sites. Conclusions : These findings indicate that diagnostic performance for vaginal dysbiosis varies by framework: Amsel criteria are more susceptible to geographical site effects, whereas Nugent score demonstrates stronger and more site-agnostic associations. For clinical studies targeting vaginal dysbiosis, Nugent scoring and/or sequencing-based approaches should be prioritized for vaginal dysbiosis endpoint definition and stratification.