Transmission networks and risk of HIV infection

12 December 2016

Research from the US Centers for Disease Control and Prevention-sponsored study known as HIV Incidence Provincial Surveillance System (HIPSS), was published in the November 30 issue of Lancet HIV.

     The study showed that sexual partnering between young women and older men, who might have acquired HIV from women of similar age, is a key feature of the sexual networks driving transmission.

     This large-scale community-wide phylogenetic study aimed to examine the underlying HIV transmission dynamics and the source and consequences of high rates of HIV infection in young women in South Africa. A cross-sectional household survey of almost 10,000 randomly selected individuals aged 15–49 years was conducted in two neighbouring sub-districts (one urban and one rural) with a high burden of HIV infection in KwaZulu-Natal, South Africa. HIV prevalence (weighted) was 59.8% in 2835 women aged 25–40 years, 40.3% in 1548 men aged 25–40 years, 22.3% in 2224 women younger than 25 years, and 7.6% in 1472 men younger than 25 years.

     HIV genotyping was done in 1589 individuals with a viral load of >1000 copies per mL. A total of 90 clusters of probable male–female transmission were identified, and within those clusters were 123 women and 103 men.

     The sexual partners of women <25 years were on average 8.7 years older, with 62% of these men aged 25 to 40, while for women aged 25 to 40 years, their sexual partners were on average just one year older. Among the men aged 25 to 40 linked to a woman under 25, 39% were linked simultaneously to a woman aged 25 to 40.

     The most probable direction of transmission among these individuals was inferred by the levels of HIV prevalence within this community. HIV transmission was most  likely to occur from high to low prevalence.

     Together, these data suggest that men aged 25 to 40 living with HIV may have acquired HIV from a woman aged 25 to 40, and that most of the women under 25 living with HIV may have acquired HIV from a man aged 25 to 40 (Figure). Over time, as the younger women grow older, this cycle is expected to continue.

     Young women are uniquely vulnerable to infection and understanding the cycle of HIV transmission for this key population is a public health imperative.

     This study provides scientific evidence to guide targeted HIV prevention interventions to break the cycle of HIV transmission and impact the course of the HIV epidemic in South Africa and potentially in other high burden settings. In particular, expansion of antiretroviral therapy and combination prevention strategies that include interventions to address age-disparate sexual partnering is crucial to reducing HIV incidence and enabling Africa to reach the goal of ending AIDS as a public health threat.