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

Vaginal dysbiosis (VD), characterized by low abundance of vaginal lactobacilli and increased bacterial community diversity, is implicated in multiple adverse reproductive outcomes and is an emerging target for preventive interventions, including live biotherapeutic products (LBPs). The most common clinical presentation of VD is bacterial vaginosis (BV), but at least half of people are asymptomatic. We investigated how two commonly used diagnostic criteria for BV, namely Amsel and Nugent, align with 16s rRNA gene sequencing-defined community state types (CSTs) demonstrating VD. We analyzed screening specimens from a Phase 1b randomized trial of LBP conducted at two sites (CAPRISA, South Africa; MGH, USA), as well as a single follow-up visit from enrolled participants. Using sequencing-based 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. Amsel BV was significantly associated with CST IV-A, and IV-B; however, the strength of association was significantly diminished at CAPRISA compared to 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. These findings indicate that diagnostic performance for VD varies by framework: Amsel criteria are susceptible to geographical site effects, whereas Nugent score demonstrates stronger and more site-agnostic associations. For clinical studies targeting VD, Nugent scoring and/or sequencing-based approaches should be prioritized for VD endpoint definition and stratification.