A recent statement from the Swiss Federal Commission for HIV/AIDS (SFCHA) stated that people with HIV receiving effective antiretroviral treatment cannot transmit HIV to their HIV-negative partner through sexual contact. But an Article published in this week's HIV Special Issue of The Lancet concludes that if such couples stop using condoms, HIV incidence could easily quadruple over 10 years.
The SFHCA statement, issued early in 2008, said that if the HIV-positive partner has undetectable levels of HIV virus in their blood (ie, less than 40 copies per ml), and no other genital infections, then that person cannot transmit HIV through sexual contact. The statement has the potential to allay exaggerated fears of transmission when the risk is actually extremely small, and could have particular value in situations such as heterosexual couples, one HIV-positive, one HIV-negative, who are attempting to conceive. But although the risk of HIV-transmission from people on effective therapy is low, it is unlikely to be zero.
Dr David Wilson, National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, NSW, Australia, and colleagues used a simple mathematical model to estimate the cumulative risk of HIV transmission from effectively treated HIV-infected patients (HIV RNA <10 copies per ml) over a long period. They investigated the risk of unprotected sexual transmission per act and cumulatively over many exposures, within couples initially discordant for HIV status (ie, one positive, one negative).
Assuming that each couple has 100 unprotected sexual encounters per year, the cumulative probability of transmission to the HIV-negative partner each year is 0.22% for female-to-male transmission, 0.43% for male-to-female transmission, and 4.3% for male-to-male transmission. In a population of 10000 discordant partnerships, over 10 years the expected number of HIV infections would be 215 for female-to-male transmissions, 425 for male-to-female transmissions, and 3524 for male-to-male transmission, corresponding to an increase in incidence of four times compared with incidence under current rates of condom use.
The authors say: "On the basis of the data presented here, we believe that the Swiss statement is not a sensible public-health message because its logical outcome would be the abandonment of condoms by people with effectively treated HIV infection…As a population strategy, treatment as prevention has the potential to reduce HIV epidemics only if consistent condom use is maintained. Indeed, our analysis suggests that there is large potential for more harm than good." They point out the recent increase in HIV infections in populations of men who have sex with men since effective treatment became available.
They conclude: "Our analyses suggest that the risk of HIV transmission in heterosexual partnerships in the presence of effective treatment is low but non-zero and that the transmission risk in male homosexual partnerships is high over repeated exposures. If the claim of non-infectiousness in effectively treated patients was widely accepted, and condom use subsequently declined, then there is the potential for substantial increases in HIV incidence."
In an accompanying Comment, Professor Geoffrey P Garnett, Imperial College London, UK, and Professor Brian Gazzard, Chelsea and Westminster Hospital, London, UK say: "In many ways the Swiss statement provides the opportunity for positive public-health messages, by promoting adherence to treatment and concern over other sexually transmitted infections. The use of condoms, in addition to antiretrovirals, to further reduce risk and prevent other sexually transmitted infections can then also be promoted."
Notes to editors: This study coincides with the release of an Australasian consensus statement from the Australasian Society for HIV Medicine (ASHM), Australian Federation of AIDS Organisations, National Association of People Living with HIV/AIDS, and the National Centre in HIV Epidemiology and Clinical Research that does not support the SFCHA claim of non-infectiousness of effectively treated patients.
Dr David Wilson, National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, NSW, Australia T) +61 421 598 939 E) Dwilson@nchecr.unsw.edu.au
Dr Geoffrey P Garnett, Imperial College London, UK T) +44 (0) 207 594 3215 E) g.garnett@imperial.ac.uk
http://multimedia.thelancet.com/pdf/press/infectiousness.pdf
Journal
The Lancet