As front-line workers in HIV prevention, it is important to understand what prevention strategies clients are using and how they understand the risks associated with them.
A common HIV prevention strategy used by gay men and other men who have sex with men (MSM) is known as "serosorting" and involves limiting all -- or just "high-risk" -- sexual activities to partners who have the same HIV status. For example, an HIV-negative person may choose to only have condomless sex with other people who are HIV negative or an HIV-positive person may choose to only have condomless sex with other people who are HIV positive. This strategy is used in the context of different types of relationships, such as stable, casual, monogamous and non-monogamous relationships.
This article focuses on how often serosorting is used, how well it works, and what can be done to make it work better.
Serosorting is quite common among MSM in Canada and other parts of the world.
Research from the United States, Europe and Australia shows that 14% to 44% of HIV-positive MSM and 25% to 38% of HIV-negative MSM engage in serosorting behaviours.1 In a 2009 survey of MSM in Vancouver, serosorting was reported by 50% of HIV-positive MSM and 34% of HIV-negative MSM.2 Furthermore, in a national survey of HIV-negative and HIV-positive MSM in Canada, condomless sex was more common in casual and regular relationships where a partner was believed to have the same HIV status and less common in relationships where a partner was believed to have a different HIV status.3
The perception in the MSM community on the effectiveness of serosorting is mixed. In the 2011/12 Male Call Canada national telephone survey of men who have sex with men, respondents were asked how effective they think serosorting is.4 According to the study, 50% of respondents thought it was effective and 50% thought it wasn't effective.
In theory, serosorting might be a highly effective strategy to reduce the risk of HIV transmission, since we know there is no possibility of HIV transmission if both partners have the same status (with the exception of superinfection for HIV-positive serosorting -- discussed later).
However, in practice, research tells us something different. While there is evidence that HIV-negative serosorting may provide some protection, there is still a relatively high risk of HIV infection among men using this strategy.
The largest study to explore the effectiveness of serosorting analyzed data from over 12,000 HIV-negative MSM in North America.5 This study defined HIV-negative serosorting as only engaging in condomless anal sex with partners who are thought to be HIV negative. The analysis found that the risk of HIV infection among "serosorters" was 57% lower compared to men who engaged in condomless receptive anal sex with partners of unknown/positive HIV status. However, the study also found that the risk of HIV infection among "serosorters" was 82% higher compared to men who did not have any condomless anal sex.
Other studies have found similar results: that serosorting generally decreases risk compared to using no prevention strategies but has a higher risk compared to using condoms consistently.6-10
The effectiveness of serosorting is likely lower than most people would expect. Incorrect knowledge of one's own, or one's partners', HIV status is the most probable explanation for this lower than expected effectiveness. If an HIV status is different from what was presumed, then the risk of HIV transmission associated with serosorting increases.
Unfortunately, research suggests incorrect knowledge of HIV status is common. There are two main reasons for this: problems with disclosure and false belief about one's own HIV status.
If disclosure of HIV status does not happen (non-disclosure), then the HIV status of a sexual partner may be incorrectly assumed.
For a variety of reasons, including privacy issues and fear of stigma, discrimination, rejection, violence or criminalization, many HIV-positive individuals do not disclose to sexual partners. Indeed, research suggests as many as 30% of MSM living with HIV don't disclose their HIV status to sex partners before engaging in condomless anal sex.11-14 Many HIV-negative MSM also do not disclose their HIV-negative status. Moreover, a substantial proportion of MSM do not ask their sexual partners about their HIV status. In a Vancouver-based survey, 36% of both HIV-positive and HIV-negative MSM did not ask the HIV status of their sex partners.2
Instead, men may make assumptions about a partner's HIV status based on indirect clues rather than directly asking/talking about HIV status (also known as implied/inferred disclosure). For example, some men may base assumptions on a partner's appearance or actions (that is, whether or not they want to use a condom) or the belief that a partner would disclose if their HIV status is different from them.1,15-17
As a result, some HIV-negative men may assume their partners are HIV negative and some HIV-positive men may assume their partners are HIV positive.18 If these assumptions are incorrect, then the risk of HIV transmission increases. Unfortunately, research suggests incorrect assumptions may be common. For example, in a study of recently diagnosed MSM, 21% reported that they were certain the sexual partner who transmitted the virus to them was HIV negative.19 Similarly, in a study of people living with HIV, many (64%) incorrectly thought their sexual partners were also living with HIV.20
While disclosure is an important step in the serosorting process, it only works if the HIV status being disclosed is accurate. While it is relatively easy to be certain of an HIV-positive status (once someone is diagnosed as HIV-positive, their HIV status is known and does not change), it can be more difficult to know for certain if one is HIV negative. Consequently, some men may incorrectly think, and disclose, that they are HIV-negative when they are not.
It is estimated that approximately 20% of HIV-positive MSM in Canada are unaware of their own HIV infection.21 These men may think and disclose that they are HIV negative and engage in serosorting behaviours based on this assumption. For example, a study from Vancouver reported that 50% of undiagnosed HIV-positive MSM thought they were unlikely or very unlikely to acquire HIV in their lifetime (despite already being infected) and 39% reported the use of serosorting to reduce their risk of becoming infected.2 In another study, approximately 20% of men who serosorted said they were HIV negative even though they hadn't been tested in the last 12 months and 16% said they didn't know their HIV status.22
It is important to consider two factors when assessing the accuracy of an HIV-negative status: the time since the last HIV test and the window period.
If someone has engaged in an activity that may have exposed them to HIV since their last HIV-negative test result, then they may actually be HIV positive. Therefore it is important to consider the length of time, and risk behaviours, since the last HIV test.
Even if someone has not engaged in any risk activities since an HIV-negative test result, it is still possible they are HIV positive due to the window period. The window period refers to the period of time from when a person first becomes infected with HIV to when a test can detect their infection. Depending on the test used, the window period can range from two weeks up to three months. During the window period, a test may incorrectly find a person who is HIV positive to be HIV negative. This incorrect test result may lead someone to assume they are HIV negative and disclose this HIV status to partners.
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