Introduction Little research has been done on the composition of the vaginal microbiota and vaginal inflammatory markers in adolescent girls and how these are affected by initiation of sexual activity.

Methods We conducted a cohort study for which we recruited adolescent girls at 4 sary schools in Antwerp. Three times over a period of 8 months, participants completed an electronic questionnaire and self-collected vaginal, rectal and oral swabs. Five vaginal Lactobacillus species, G. vaginalis, and A. vaginae employing qPCR; eight inflammatory markers by Luminex; and BV by Nugent score 7–10 were measured in the vaginal specimens. In the oral and rectal specimens, measurements were limited to Lactobacillus genus,G. vaginalis, and A. vaginae. The association of sexual activity (none, penetrative sexual intercourse and non-penetrative activity) with the vaginal, oral and rectal microbiota, BV and vaginal inflammatory markers was assessed by bivariate analysis.

Results Of the 93 adolescents (14–20 years), 53 (57%) were virgins, 35 (37.6%) had had penetrative sexual intercourse and 5 (5.4%) had engaged in non-penetrative activity. Cross-sectional, sexual activity was associated with an increased presence of vaginal G. vaginalis (p = 0.016), rectal G. vaginalis (p = 0.027), and rectal A. vaginae (p = 0.010); with higher IL-1α (p < 0.001), IL-8 (p = 0.002) and MIP-1β (p = 0.030); and with BV (p = 0.009). During follow-up, 9 (9.7%) participants had penetrative sexual intercourse for the first time. At individual level this was associated with a higher IL-1α (+0.37 log; p = 0.010) compared to girls who remained virgin over the three visits. Similarly, in girls who reported sexual intercourse IL-1α and IL-8  was higher (+0.39 log; p < 0.0001; +0.43 log; p = 0.003) compared to the virgins.

Conclusion Sexual debut is associated with the presence of BV related species and the inflammatory status of the vaginal milieu. Consequently, around this period in life adolescent girls have increased vulnerability to HIV and other sexually transmitted infections.

Disclosure of interest statement This work was supported by the European Commission on the grand Combined Highly Active Anti-Retroviral Microbicides (CHAARM) N° 242135. No pharmaceutical grants were received in the development of this study.