The male partners of HIV-positive women are more than twice as likely to become infected with HIV themselves if their partner becomes pregnant, the 2010 International Microbicides Conference heard today.
The study also found that HIV-negative women were twice as likely to become infected by their positive partner if they became pregnant. However, in this case the increase in HIV incidence was largely accounted for by the fact that pregnant women were on average younger (and therefore more biologically vulnerable to HIV), more likely to be having unprotected sex, and less likely to be using oral contraceptives.
In the case of the men the significance of the result actually became slightly stronger after adjusting for age, unprotected sex, circumcision status and the partner’s viral load and CD4 count. This implies that pregnancy in HIV positive women is an independent risk factor for increased transmission.
This result is one of a series of findings that have come out of the Partners in Prevention Study. This study, which randomised people with HIV to receive aciclovir or placebo to see if suppressing herpes (HSV-2) infection might reduce HIV transmission, failed in its primary aim.
However it has produced a number of other ‘spin-off’ results which tell us a lot about HIV transmission risk between heterosexuals, including a study presented at CROI in February which showed that HIV treatment reduced transmission by 92%.
The present study involved 3321 heterosexual ‘serodiscordant’ couples (one partner HIV-positive and the other not). In two-thirds (67%) of the couples the woman was the HIV-positive partner.
During the trial there were 823 pregnancies of which 503 (61%) were in women with HIV. Sixty-four women acquired HIV during the study (annual incidence: 3.8%) and 57 men (annual incidence 1.7%). Twenty-seven per cent of infections in women occurred when they were pregnant and 21% of infections in men when their partner was pregnant.
Women were 2.1 times more likely to acquire HIV when they were pregnant (95% confidence interval (CI) 1.2 to 3.7, p=0.009). However, this lost significance after adjustment (HR 1.53, 95% CI 0.84 to 2.77, p=0.2).
Men were 2.21 times more likely to acquire HIV when their partner was pregnant (95% CI 1.17 to 4.19, p= 0.02) and this increased risk remained significant after adjustment (HR 2.28, 95% CI 1.16-4.46, p=0.02).
Increased female-to-male transmission of HIV during pregnancy may be due to physiological and immunological changes that occur with pregnancy, the authors conclude, but more research will be needed to confirm this hypothesis.
Mugo N et al. Pregnancy is associated with an increased risk of HIV transmission among African HIV-1 serodiscordant couples. 2010 International Microbicides Conference, Pittsburgh, abstract 8, 2010.