Incubation Period and Risk Factors Support Sexual Transmission of Bacterial Vaginosis in Women Who Have Sex with Women

Objective: The epidemiology of bacterial vaginosis (BV) favours sexual transmission of BV-associated bacteria. We examined incubation period and risk factors for incident BV (iBV) in a prospective study of women who have sex with women (WSW).

Methods: Using daily self-collected vaginal swabs, WSW with normal vaginal microbiota (no Amsel criteria and a Nugent score of 0-3) were followed for 90 days or until iBV (Nugent score 7-10 on at least 2-3 consecutive days). Daily diaries of sexual activity and menses were completed. Time to iBV was estimated. Accounting for differing lengths of follow-up and age, rates of sexual activities (per 100 person-days (pd)) were compared according to iBV status. The relationship between menses and iBV was also investigated.

Results: Of the 36 WSW, the mean age was 30 years (SD 8) and 92% were African American. The probability of iBV at 30 and 60 days was 20% (SD 7%) and 36% (SD 8%), respectively; 14 (39%) developed iBV by 90 days. In WSW with iBV versus those without iBV, the relative rate of any sexual activity prior to iBV was 40% higher (20.4 vs 14.6 per 100 pd; p=0.010), sex with a woman was 38% higher (14.3 vs 10.3 per 100 pd; p=0.038), digital-vaginal sex was 57% higher (14.3 vs 9.1 per 100 pd; p=0.005) and digital-anal sex was 5.6 times higher (2.9 vs 0.5 per 100 pd; p<0.001). iBV was more likely for those WSW with menses in the prior 2 days as compared with those without recent menses (HR 3.4; p=0.029). Sexual activity occurred in 93% WSW at a median of 4 days (95% CI 2 to 6) prior to iBV.

Conclusion: iBV was common and associated with sexual activity in this cohort of predominantly African American WSW. An incubation period of 4 days is consistent with other bacterial STIs.