Longitudinal Changes in Vaginal Microbiota Composition Assessed by Gram Stain Among Never Sexually Active Pre- and Postmenarcheal Adolescents in Rakai, Uganda

Study Objective: To describe changes in vaginal microbiota and pH over time among never sexually active adolescents at different menarcheal stages. Design: A cohort of 49 sexually inexperienced Ugandan adolescents provided weekly self-collected vaginal swabs and behavioral/health information for up to two years. Menarcheal stage was classified as: not experiencing menarche during follow-up (premenarcheal, n = 9), achieving menarche during follow-up (perimenarcheal, n = 20), and being postmenarcheal (n = 20) at enrollment. Vaginal microbiota were characterized as morphotypes of large gram-positive rods, small gram-negative or variable rods, and curved gram-negative rods based on Nugent Gram-stain criteria. Baseline measures were compared using nonparametric tests. Mean changes (β) in morphotypes and pH over time were estimated using longitudinal mixed-effects models. Results: The baseline median (IQR: interquartile range) Nugent score was 8 (7-8) in premenarcheal, 4.5 (1-8) in perimenarcheal, and 1 (0-3) in postmenarcheal girls (P = 0.001). For each respective menarcheal stage, the median (IQR) counts of gram-positive rods were 0 (0-0), 10 (0-30), and 30 (18-30) (P = 0.002) and gram-negative or variable rods were 30 (30-30), 16 (0.5-30), and 0.5 (0-2.5) (P = 0.002) at enrollment. Counts of gram-positive rods increased (β = 0.259, 95% CI: 0.156, 0.362) and gram-negative or variable rods decreased (β = -0.201, 95% CI:-0.298,-0.103) significantly over time in premenarcheal girls, but not in other groups. Vaginal pH declined significantly in peri- and postmenarcheal girls only. Conclusion: Vaginal microbiota composition varied by menarcheal stage at enrollment. Over time, significant changes in vaginal morphotypes occurred in premenarcheal girls, suggesting this may be an important period of transition.