A new study that measures the importance of different routes of transmission in 18 African countries and regions provides support for an aggressive "test and treat" approach which would seek to identify and offer treatment to all HIV-positive individuals in Africa.
"By investigating what can be learned about routes of heterosexual transmission in sub-Saharan Africa from large-scale survey data we found that pre-couple, within-couple and extra-couple transmission are all important," says Jonathan Dushoff, associate professor of biology at McMaster University; member of the Michael G. DeGroote Institute for Infectious Disease Research, and senior author on the study released online this week by the journal Lancet.
Using a mathematical framework, the research provides evidence that effective public-health approaches against HIV should take a broad, population-based approach. The study was led by Steve Bellan, who was completing his Ph.D. at the University of California, Berkeley and is now postdoctoral researcher at the University of Texas.
Recently a new antiretroviral therapy was developed to prevent HIV transmission from an HIV-positive individual to his or her partner by reducing the amount of virus in the body. The World Health Organization now recommends that this "test and treat" strategy be given to all HIV-positive individuals who are in a relationship with HIV-negative partners. In fact, despite its expense and logistical demands, the approach is currently under consideration and will be tested shortly in community-wide randomized controlled trials.
"Incredible progress has been made in preventing HIV transmission, and researchers are continuing to make major discoveries," said Bellan.
Added Dushoff: "Our goal was to quantify the amount of transmission that occurs through various routes, and increase the amount of specific information available to policy makers deciding how to allocate resources to various prevention strategies."
To conduct their study, the researchers constructed a mathematical model of demographic and health survey data from more than 27,000 couples in 18 countries across sub-Saharan Africa to better assess the proportion of new infections caused by extra-couple transmission. The group avoided relying on self-reported sexual activity, but instead used information on relationship length and timing, how long partners were sexually active before entering their current relationship, and couples' testing results to infer the risks of transmission through different routes.
"Everyone lies about sex," said Dushoff. "We wanted to rely on answers to questions that people are likely to answer accurately."
The researchers used these inferences to estimate what proportion of HIV transmission occurred: between members of surveyed couples; before those couples were formed; or through "extra-couple contacts" (that is, sexual contact with outside individuals during the partnership). The researchers say that as plans to use antiretroviral drugs as a strategy for population-level prevention progress, understanding the importance of different transmission routes is crucial to target intervention efforts.
"To efficiently address the HIV epidemic, health policies should not only focus on couples where one partner is HIV-positive, but should reach out to all sexually active individuals," said Bellan.
According to the World Health Organization, in 2011, 2.5 million people were newly infected with HIV and an estimated 1.7 million people died. However, because of new prevention strategies, there were 700,000 fewer new infections worldwide than 10 years ago, and 600,000 fewer deaths than in 2005.