About half of new HIV cases occur when the person transmitting the virus is in the early stages of infection and unlikely to know if he or she is HIV-positive, according to a study scheduled to be published in the April 1 edition of the Journal of Infectious Diseases, Toronto's Globe and Mail reports (Priest, Globe and Mail, 3/2). For the study, researchers led by Mark Wainberg of the McGill University AIDS Centre conducted phylogenetic analysis -- a genetic analysis that clocks the virus' mutations to estimate the initial date of transmission -- among HIV-positive people in Quebec. They found that 49% of cases were clustered in a way that suggested they had been transmitted by people who recently became HIV-positive. When people first become HIV-positive, they have high viral loads, which increases the chances of transmitting the virus, Reuters Health reports. "The early infection stage can be entirely asymptomatic," Wainberg said, adding, "This is why people who are recently infected may not know it and will probably often test negative by conventional antibody screening" (Reuters Health, 3/5). Most people test positive for HIV two to four weeks after exposure; however, some people do not test positive until three to six months after exposure, according to Rita Shahin, associate medical officer of health at the Toronto Public Health Department. The study is raising questions in the medical community about how to identify people at high risk of contracting HIV for frequent HIV testing and whether people at an increased risk should begin taking antiretroviral drugs as a preventive measure, the Globe and Mail reports.

Reaction
Shahin said the study is "important," adding, "We've always known that people who don't know their HIV status are accounting for a significant percentage of transmissions. This further narrows it down to that group who are in the first six months of infection." Shahin recommended that people at high risk of HIV exposure be tested every three to six months (Globe and Mail, 3/2). Wainberg said the medical community "must do a much better job of identifying recently infected people if we are to be able to counsel them to modify high-risk sexual behavior and desist from transmitting the virus" (Reuters Health, 3/5). Wainberg added that clinical trials are underway to determine if antiretrovirals could help prevent HIV transmission among high-risk groups, such as commercial sex workers, in developing countries (Globe and Mail, 3/2).

Related Commentary
In a related editorial commentary, Deenan Pillay of University College London and Martin Fisher of the Department of HIV/Genitourinary Medicine at Brighton and Sussex University Hospitals write that the medical community should consider highly active antiretroviral therapy to prevent HIV transmission. Pillay and Fisher write that HAART should not be used as a substitute for other preventive measures that focus on behavior but add that the "current focus on increasing HIV diagnoses through more widespread testing requires a parallel strategy for minimizing ongoing transmission" (Fisher/Pillay, Journal of Infectious Diseases, 4/1).

The study is available online.

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