In this cohort of women reporting sex with women, rates of vaginal colonization with two species of commensal H2O2-producing lactobacilli four weeks after treatment for bacterial vaginosis were low. Though colonization was infrequent, women who were able to establish colonization achieved high concentrations of each of these bacteria.
For clinicians and affected women, the high rate of BV recurrence after antibiotic treatment is exceedingly frustrating [10
]. Several groups have evaluated whether adding probiotic compounds containing lactobacilli to treatment improves outcomes, but results have been mixed [33
]. In a study of healthy women treated with vaginal probiotic capsules containing L. crispatus
, participants who reported penile-vaginal sex between treatment and followup were less likely to establish colonization with the probiotic strain [37
]. We hypothesized that sexual activity in the month after treatment may inhibit vaginal colonization with beneficial lactobacilli, possibly through reinoculation with BV-associated bacteria from vulvar or rectal reservoirs, which might increase risk for BV recurrence.
In the parent study of nearly 350 women from which this nested case control study was derived, we demonstrated that women cured of BV had higher rates of colonization by L. crispatus
after treatment (42%) than women with persistent BV (26%;P
= .0003); data on L. jensenii
were not available [30
]. A different study obtained vaginal swabs for culture and found that by 4 weeks after treatment with vaginal metronidazole 59% of women were colonized with hydrogen peroxide producing lactobacilli [20
]. Other studies used Nugent score to characterize shifts of the vaginal bacteria, and reported that as many as 66% of treated women had at least some lactobacilli at 21–30 days after treatment [38
], though H2
production was not measured. Our group previously measured posttreatment quantity of L. crispatus
in a cohort of pregnant women using PCR and found that only 9/53 (17%) of women had detectable levels 4–6 weeks after treatment [39
Few studies have evaluated behavioral predictors of colonization with lactobacilli. In women with BV, those who report more sexual partners are less likely to be colonized with H2
-producing lactobacilli [40
]. In our cohort, women colonized with L. crispatus
who reported digital-vaginal and/or oral-vaginal sex had lower quantities of this bacterium. Although it did not reach statistical significance, we saw a paradoxical opposite trend in the risk related to these behaviors for vaginal colonization with L. crispatus
or L. jensenii
, suggesting that women with more partners, or reporting more frequent oral-vaginal or digital-vaginal sex, were more likely to be colonized. One possible explanation is that women colonized by L. crispatus
and L. jensenii
more likely achieved cure of BV, thus reducing the likelihood of vaginal symptoms that might deter them from engaging in sex. This observation highlights the difficulty in studying the complex relationships between sexual behaviors and the dynamic nature of vaginal microbiology—temporal associations are difficult to ascertain unless both outcomes are measured frequently (ideally, daily).
The main limitation of this study is the small sample size, which reduced our power to detect potential associations between behaviors and colonization with specific lactobacilli. A significant number of participants with BV did not have a posttreatment sample, which limited our ability to examine the entire study group. Participants selected for this substudy were similar to the larger cohort except for having higher Nugent scores at diagnosis, which may partially explain their high rate of treatment failure. This cohort is composed primarily of women who have sex exclusively with women, and our results may differ from those obtained in a cohort of primarily heterosexual women. However, this allowed us to study the effect of several different types of sexual behavior on the vaginal microbiota. The population had well-characterized information about sexual activity during the treatment period, and a very high rate of followup (92%). Our quantitative PCR analysis allowed detection of small quantities of bacteria and analysis of changes in quantity of bacteria after treatment with respect to sexual behaviors.