There is generally a strong association between levels of HIV in the blood and in the female genital tract, and the virus is most likely to be ‘shed’ in the cervical and vaginal fluidswhen a woman has a high blood viral load^[1]. However, as with men, viral load may be higher or lower in the genital fluids compared with the blood.

Unlike blood viral load, HIV viral load in the female genital tract varies over the course of the menstrual cycle, even among women on treatment^[2]. Some research suggests that use of hormonal contraceptives can also increase genital shedding of HIV^[3].

Antiretroviral therapy usually reduces HIV viral load in cervical and vaginal fluids. In one recent study, for example, HIV viral load in cervical and vaginal fluids declined steeply within two to four days after starting HAART, and became undetectable within two weeks. But a proportion of women with undetectable blood viral load - perhaps one-third - still shed HIV in their genital secretions despite otherwise effective antiretroviral therapy, posing a continued risk for sexual and mother-to-child transmission ^[4][5].

Although there have been fewer studies in women than men, research indicates that levels of some antiretroviral drugs may fail to reach effective levels in the female genital tract. One recent study suggested that women who took NNRTIs were more likely to have continued cervical shedding of HIV than those who took protease inhibitors^[6]. Further, cervical and vaginal fluids may harbour HIV variants with different drug-resistant profiles than those seen in the blood.