Bacterial vaginosis appears to be more common, and genital warts less common, among women who have ever had sex with women than among women without same-sex experience. The gender of a woman's recent sexual partners, however, does not seem to affect her likelihood of having an abnormal Pap smear result. According to a case-control study that examined data from a sexually transmitted infections (STI) clinic in Sydney, Australia,¹ the prevalence of both sexual and nonsexual behaviors that increase the risk of HIV is significantly higher among women who have had sex with women than among other women.

The records of new female clients who sought care at the inner-city, public clinic from March 1991 through December 1998 were used in this cross-sectional study. Overall, 1,423 clients (10% of the clinic's total registration over the period) reported any female-female sexual activity. The researchers excluded transsexual women and clients whose same-sex relations occurred only in the context of sex work, and compared the remaining 1,408 women who reported ever having had sex with a woman with 1,423 clients without such experience.

The median age among both groups of clients of the STI clinic was essentially the same (27 years for cases and 26 years for controls). Although women who have had sex with women were significantly less likely than other women to cite having genital symptoms as the reason for their visit (19% vs. 23%), cases were more likely than controls to have come to the clinic to request a Pap smear (7% vs. 5%). Moreover, clients who had had sex with women were twice as likely as other women to currently be sex workers (22% vs. 11%).

For each group of women, the investigators assessed the incidence (taken retrospectively from clinic records) of an abnormal Pap smear result and of diagnosis with an STI (bacterial vaginosis, genital herpes and warts, gonorrhea, chlamydia, candida, hepatitis B and C, and HIV). They also considered whether women in each group had engaged in several sexual and nonsexual risk behaviors.

According to results of a univariate analysis, women who had had sex with women were significantly more likely than controls to test positive for bacterial vaginosis (8% vs. 5%), but were significantly less likely to have newly diagnosed genital warts (8% vs. 11%). There was no difference between the two groups in the proportion whose cervical cytology (Pap smear) was abnormal or who tested positive for genital herpes, chlamydia or candida. And while cases were significantly more likely than controls to have a self-reported history of STIs (44% vs. 32%), there was virtually no difference between the two groups in their rate of HIV infection (less than 1% in both groups). Women who had ever had female- female sex were far more likely than controls ever to have injected drugs (23% vs. 4%) and to have had sexual contact with an injection-drug user (21% vs. 6%); consistent with these findings, they were significantly more likely to have ever had hepatitis C (5% vs. less than 1%) or hepatitis B (5% vs. 3%).

Clinic clients who had ever had sex with women were also significantly more likely than controls to have had an induced abortion (38% vs. 27%). The vast majority (93%) of women with same-sex experience had also had a male sexual partner, and their median number of male partners was significantly higher than that among other women (12 partners vs. six). In fact, women who had had sex with women were significantly more likely than other women to have had more than 50 lifetime male partners (9% vs. 2%). Moreover, sexual contact with a homosexual or bisexual man was significantly more likely among women who had had sex with women than among clients with no such experience (15% vs. 5%).

Among the cases, the researchers identified a subgroup of 283 women whose sexual partners had been exclusively female for the past year. The STI and risk profile of these women (of whom 25% had never had sexual contact with a man) was similar to that of the overall group of cases. They were even more likely than all cases, however, to have bacterial vaginosis (10% vs. 8%). This subgroup of cases did not differ from cases overall in their prevalence of hepatitis C infection; by extension, this means that they too were significantly more likely than controls to test positive for this blood-borne virus. The rate of infection with hepatitis B was higher among women whose sex partners in the past year were exclusively female than among controls. This subgroup of cases was similar to controls, however, in their likelihood of having an abnormal Pap smear.

The researchers used unconditional logistic regression analysis to determine which risks and behaviors were independently associated with ever having had female-female sexual contact, controlling for factors that were significant at the univariate level or that are considered to be potential confounding factors in the literature. Net of all variables, two STI diagnoses were independently associated with female-female sexual contact--bacterial vaginosis (odds ratio, 1.5) and genital warts (0.7). Five risk behaviors were independently and positively associated with female-female sexual contact-- having had sex with a homosexual or bisexual man (odds ratio, 2.5) or with an injection-drug user (2.1), having had more than 50 lifetime male partners (3.4), having had an abortion (1.4) and current or previous injection-drug use (5.0).

The investigators comment that their study is limited by its reliance on a nonrepresentative population of STI clinic patients and by its lack of data on specific sexual practices (which might shed light on why odds ratios for a diagnosis of bacterial vaginosis were significantly elevated for women who had had sex with women). Nonetheless, they conclude that their data "argue strongly for increased measures to improve our understanding of the sexual health" of women who have had sex with women.

A related editorial mentions that the study is noteworthy in demonstrating an "alarming prevalence" of HIV-related risk behaviors in women who have had sex with women.² The author warns that such women, although traditionally considered "low-risk," may, in fact, act as a bridge population for transmission of the virus because of their sexual links to men who may themselves be at high risk. This "provocative evidence" is important, the editorial argues, because traditional assumptions that female-female sex confers little risk and that the area is not worthy of study have meant that data on the epidemiology of STIs in women who have had sex with women are seriously lacking. --L. Remez

References

1. Fethers K et al., Sexually transmitted infections and risk behaviours in women who have sex with women, Sexually Transmitted Infections, 2000, 76(5):345-349.

2. Marrazzo JM, Sexually transmitted infections in women who have sex with women: who cares? editorial, Sexually Transmitted Infections, 2000, 76(5):330-332.