HAART works by dramatically reducing levels of HIV in the blood and tissues. This, in turn, allows the immune system to begin repairing itself,
leading to increased numbers and better functioning of T-cells and other parts of the immune system.
Some researchers have theorized that if many HIV-positive people in a community take HAART, it may reduce their sexual infectiousness at a
population level-thousands of people. Preliminary findings from observational studies with heterosexual people in Southern Africa and injection drug users in
Vancouver suggest that HAART is able to do this in the short-term. However, because of their study design, it is difficult to draw firm conclusions-that is,
to prove a link between cause (taking HAART) and effect (reduced risk of HIV transmission)-in observational studies. Firm conclusions about the impact
of HAART on HIV transmission, at least in heterosexual couples, will be obtained from an international clinical trial called the Strategies in
Timing of AntiRetroviral Treatment (START). This is because part of START will assess HIV transmission in sero-discordant couples.
Most data on estimated risk of HIV transmission comes from heterosexual couples. Using this data, some researchers have theorized that HAART may be
able to reduce the risk of HIV transmission among gay and bisexual men. However, there may be sexual and biological reasons why the risk of HIV transmission is greater among
gay and bisexual men than it is among heterosexual couples.
To try to understand the risk of HIV transmission among men who have sex with men, researchers in Australia undertook a prolonged study. Their analysis is disquieting, suggesting
that the overall risk of HIV transmission among gay and bisexual men has not changed in the era of widely available HAART.
The research team was surprised by its findings, particularly because HAART is widely available and access to health care is subsidized in Australia. Moreover,
the availability of HAART was supposed to, in theory, reduce the risk of HIV transmission at the community level because many men who use HAART should have viral loads less
than 50 or 40 copies/ml in the blood.
The Australian researchers suggested the following possible reasons that may account for their findings:
It is possible that most new HIV infections are inadvertently spread by people who are themselves recently infected (and who are highly infectious) and are unaware of their infection.
It may be possible, they noted, that "HIV transmission by anal intercourse is not as closely related to viral load as it is in vaginal transmission." In other words, it may be easier to
transmit HIV via anal intercourse than vaginal intercourse. This is not surprising because when women are sexually aroused the vagina can produce lubrication, which reduces friction and
damage to the vagina during sex. There is no equivalent response in the anus and insufficient lubrication may predispose the anus to microscopic cuts during sex, providing an entryway
for HIV to get into the body. Furthermore, since the beginning of the AIDS epidemic, unprotected anal sex among men has always been associated with a high risk of HIV transmission
compared to other sex acts.
In Australia and other high-income countries including Canada, rates of sexually transmitted infections (STIs) among gay and bisexual men appear to be greater now than they were
before 1996. STIs, by causing inflammation, sores or lesions on or inside delicate genital tissue, may increase the risk of HIV transmission. A combination of increased high-risk
sex and increased STIs may have overwhelmed any ability of HAART to prevent HIV transmission, at least at the community level among gay and bisexual men in the Australian study.
Not mentioned by the Australian research team is this: Separate groups of scientists in Canada, the European Union and the United States have found that HIV can be detected
in the semen of men who have been taking HAART, who are free of STIs and whose viral load in the blood is less than 50 or 40 copies/ml.
See our previous CATIE News story
for more information about these studies.
Recent reports from Amsterdam, New York and San Francisco suggest that HIV infection has become as common as or even more common among some gay or bisexual men than
it is in the generalized HIV epidemics of sub-Saharan Africa. Taken together, the findings from Australia and other countries suggest that HAART may not greatly reduce the risk
of HIV transmission at the population or community level, at least among gay and bisexual men.
1. In people who are adherent to HAART and who do not have STIs, HAART will reduce levels of HIV in the blood and sometimes in the semen (and likely other genital fluids).
However, the risk of HIV transmission is not eliminated nor is it negligible. Indeed, sexual transmission of HIV has occurred in multiple cases when viral load in the blood
was less than 50 copies/ml. Use of condoms remains the best way for sexually active adults to prevent the transmission of HIV.
2. HAART has potential for slowing the spread of HIV among gay and bisexual men. However, if a sufficient proportion of gay and bisexual men engage in high-risk
behaviour, HAART's potential for HIV prevention may be very limited. This may be the case, as in the past 10 years researchers have found that rates of STIs,
particularly syphilis, have soared together with reports of high-risk behaviours in several high-income countries. Both of these factors increase the
risk of transmission and likely overwhelm the protective effect of HAART at the level of the community.
We thank the many researchers, including experts in infectious diseases, internal medicine, biostatistics and other specialties across Canada, the European Union
and the United States who contributed their time for helpful review, discussion and research assistance.
-Sean R. Hosein
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CATIE-News is written by Sean Hosein, with the collaboration of other members of the Canadian AIDS Treatment Information Exchange, in Toronto.
From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at http://www.catie.ca
Source: CATIE: CANADIAN AIDS TREATMENT INFORMATION EXCHANGE