Among white women, we found that those who had an African-American male sex partner were approximately twice as likely to develop BV as those who reported only white male sex partners. The probability of BV appearing was similar in African-American (26.6%) and white (24.8%) women in the presence of an African-American male sex partner. Consistent condom use appeared to blunt the association between African-American male sex partners and BV acquisition among white women. These results suggest that BV has a sexual network component.
We are aware of only one previous study addressing the association of the both the woman’s and her male partner’s race and BV. In that cross-sectional study of women in the first trimester, Simhan et al.12
found that among white women, BV was approximately twice as prevalent when the father of the pregnancy was African-American than when he was white, but the father’s race was not strongly associated with BV among African-American women. Our longitudinal results are in agreement with Simhan’s regarding white women although we could not study this association in African-American women.
Whether BV is a sexually transmitted infection is controversial. Supporting non-sexual transmission are the observations that a single pathogen has not been identified as causing BV;6
that BV is regularly observed in self-reported virginal women,10,18,19
that personal hygienic behaviors such as douching are associated with an increased risk of BV8
and that co-treatment of male partners did not impact recurrence of BV.20
Supporting sexual transmission is the frequent co-occurrence of BV and infections known to be sexually transmitted;21
the increased prevalence of BV among women with more sex partners;22
increased BV incidence in the presence of a new sex partner;23
increased number of recent sex partners among male partners of women who developed BV;24
the high concordance of BV in lesbian sex partners;25
and results of a randomized trial indicating that male partner circumcision reduces the risk of BV.26
The association between BV and condom use has been variable. In a previous report from the Flora study, condom use was not associated with reduction in BV.27
However, other studies found recurrent BV was less common in women who abstained from sex or consistently used condoms;28
that BV treatment failure was more common when there was unprotected sex;29
that isolation of Gardnerella vaginalis
from the urethra was reduced among men who consistently used condoms;30
and that BV occurrence was less during times when a woman consistently used condoms compared to times when that same woman did not use them consistently.31
Our finding that a characteristic of the male partner, his race, is associated with occurrence of BV might support sexual transmission, and the finding that consistency of condom use minimized this association further supports sexual transmission either of an infectious agent or other exposure in semen. Although BV is more prevalent among African-American women than among women of other racial groups,10
race is a social, rather than biological construct.32
Nevertheless, in nationally representative surveys only small minorities of both African-American and white individuals reported sexual relationships with individuals of the other race.33
Modeling of STD transmission in nationally representative data has shown that among individuals with one partner, the chance of the partner being in the “STD transmission core” is greater for African-Americans than for non-African-Americans.34
In combination with the observed degree of “sexual segregation” this results in higher prevalence of bacterial STDs in the African-American community, even after controlling for individual-level behaviors.34
We observed that the increased occurrence of BV associated with an African-American sex partner was greatest among women who had more than a high school education. There may be non-sexual factors (such as poor nutrition,35
) associated with acquisition of BV, and these factors are more prevalent among less educated women. Decreased occurrence of these non-sexual risk factors among more educated women would increase the apparent relative risk of sexual risk factors among these women by removing non-sexual causes of BV.
Strengths of the study include the prospective design, which enabled us to ascertain the appearance of BV, and the collection of detailed data on sexual habits. However, there are limitations. While we collected relatively extensive data about study women, and controlling for these potentially confounding factors did not substantially change our results, there may be unmeasured behaviors or characteristics that are adopted by white women who have African-American sex partners, that are otherwise more common among African-American women and that are the true cause of BV. In particular, our measure of socioeconomic status was limited to years of education. White women who have African-American sex partners may differ on other, more subtle socioeconomic characteristics than white women who have only white sex partners. We did not collect detailed data on male sexual partners, including socioeconomic factors like education or occupation, nor did we collect data on partners’ sexual histories. Adjustment for this information, had it been available, might have reduced the risk ratio.
Partners’ race was reported by the woman; while women were unaware of their BV status at the time of interview and reporting error is unlikely to differ by BV status, erroneous reporting is possible. Such non-differential misreporting would on average result in a lower risk ratio than we might otherwise have observed. We asked about condom use over the past 30 days, rather than during the entire 3-month interval. We ascertained BV only at the beginning and end of each 3-month interval. Women who were BV-negative at the beginning and end of the interval might have had BV at some point between those dates; similarly we do not know whether, within any given interval, intercourse preceded the appearance of BV.
An additional limitation arises from the chronic nature of BV. Regardless of its mode of acquisition, once established, BV often recurs in spite of treatment,36
and can have a relapsing and remitting course in untreated women.37
We followed women for one year. Women who were BV-negative at the beginning of the study might have had BV before they enrolled, blurring the distinction between “incidence” and “relapse.” Similarly, the characteristics of a woman’s sex partners over the course of the study might not be the same as those of any partners she may have had before she enrolled. To address this limitation it would be necessary to begin following women before they become sexually active.
In summary, our findings that the race of a woman’s male sex partner is associated with the appearance of BV, and that consistent use of condoms appears to mitigate this association provides indirect evidence for a sexual network and transmissible nature of BV.