HIV transmission rate ten times higher during primary infection

An unequivocal link between recent HIV-infection and high risk of HIV transmission was reported on Tuesday at the Tenth Conference on Retroviruses and Opportunistic Infections in Boston.

The researchers calculated the incidence of HIV transmission per monogamous, vaginal heterosexual act as thus: in the five months immediately following seroconversion, rate of transmission was ten times greater than during chronic infection at 8.2 per 1000. In late stage infection (five to 15 months before death) it was 4.5 per 1000. During chronic infection, once the viral load set point had been reached - after 5 months and before late stage HIV disease - the transmission rate was 0.8 per 1000.

Although it has been understood for some time that there was an association between the very high viral loads seen during the primary infection and a greater likelihood of infecting others, this report from the Johns Hopkins University Rakai Project Team suggests that much HIV prevention work would benefit greatly by focusing on those currently untested or very recently infected.

The team had previously published preliminary findings in The Lancet that concluded higher viral load and genital ulceration were the main determinants of HIV transmission amongst 174 monogamous, heterosexual, serodiscordant couples in rural Uganda.

Yesterday’s report included data from 240 out of 443 serodiscordant couples retrospectively identified from the 1995-99 community-based study. There was a larger proportion (184 vs. 56) of male to female index partners (the index partner is the initial HIV-positive partner of the couple) since the HIV-negative partner had to report no extramarital activity during the course of the study.

At the start of the trial 166 index partners were already HIV-positive (the chronic index group); 23 index partners seroconverted during the study (the early index group); and 51 index partners died during the study (the late stage index group). This allowed the researchers to separate early, chronic and late stage HIV transmission risks.

During the study, 24% of the partners of the chronic index group seroconverted. This more than doubled to 56% (13/23) of the partners of the early index group, of which 10 (43%) seroconverted within the first five months of their partner’s seroconversion. At 37%, the seroconversion incidence of the partners of the late stage index group was somewhere in-between.

During the question and answer session following the presentation, it was revealed that consistent condom use was only 3%, despite counselling. When condoms were used, they provided a similar protective effect to male circumcision, which was seen to halve the rate of transmission during chronic HIV infection to 0.4 per 1000 compared with uncircumcised men, but which was not seen to be protective during early and late stage infection when viral loads were much higher. Finally, the researchers saw no statistical difference between the direction of HIV infection i.e. females could transmit HIV as efficiently as males during vaginal sex.