Bacterial vaginosis, high-density group B streptococcus colonization, and the use of hormonal contraceptives are all independently associated with increased risk of genital tract shedding of herpes simplex virus type 2, Thomas L. Cherpes, M.D., and his colleagues at the University of Pittsburgh reported.
These increased risks could be key factors in HSV-2 transmission.
“Because hormonal contraceptives are used by more than 100 million women worldwide, and because bacterial vaginosis and vaginal GBS colonization are two of the most common genital tract conditions present among women of reproductive age, even modest associations between these variables and genital tract shedding of HSV-2 would result in substantial attributable risks for transmission of the virus,” they reported (Clin. Infect. Dis. 2005;40:1422–8).
The researchers followed 330 HSV-2-positive women for a year. The women were aged 18–30 years; 65% were black. Every 4 months, the investigators collected behavioral data, vaginal swabs and smears, and a blood sample from each woman.
In the multivariate analysis, genital tract shedding was associated with recent HSV-2 seroconversion (odds ratio [OR] of 3), high-density group B streptococcus colonization (OR 2.2), bacterial vaginosis (OR 1.9), and the use of either depomedroxyprogesterone acetate or oral contraceptives (OR 1.8).
Genital tract shedding was not associated with vaginal intercourse, having a new sex partner, or douching.
The associations with bacterial vaginosis and high-density GBS colonization were somewhat of a surprise, the researchers said. “A number of recent studies have demonstrated that [bacterial vaginosis] is associated with significant alterations in the concentrations of several immunomodulatory cytokines, compared with the concentrations of these cytokines associated with normal vaginal flora.”
Oral contraceptives may influence shedding by different means, the researchers said. Suppression of estrogen and progesterone may alter the T cell-mediated immune response, and thereby increase shedding.
Additionally, women who use oral contraceptives can have larger areas of cervical ectopy. “This extension of the single-layered columnar epithelium onto the ectocervix may facilitate genital tract shedding.”
However, since the increased risk was the same for both oral and injectable hormonal contraceptives, and cervical ectopy is more commonly associated with the oral form, it may not be the predominate mechanism responsible for increased viral shedding, they said.
Previous studies on the subject have reached varying conclusions, Katherine LaGuardia, M.D., medical affairs director for Ortho Women's Health, Ortho-McNeil Pharmaceutical, Inc., said in an interview.
“This study really doesn't shed any new light on this issue,” she said. “The definitive study, which would control for both sexual behavior and hormonal contraception, has yet to be done.”
However, it's important to continue emphasizing to women that no hormonal contraceptive method protects against sexually transmitted infection, Dr. LaGuardia said.
“Although safe and effective when used as labeled, these methods don't protect against infection,” she added. “Using a condom along with hormonal methods offers the best protection against both pregnancy and STIs, including HIV,” Dr. LaGuardia explained.