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

Abstract

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.