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New Directions in HIV Prevention: Serosorting and Universal Testing

February 2006

New Directions in HIV Prevention: Serosorting and Universal Testing
The use of HIV testing and information about one's serostatus as an HIV prevention tool remains a complex and controversial area of debate, largely due to issues of trust: trust in the confidentiality of information, trust that health care providers will not test without consent, and trust that partners are telling the truth about their status. For all these reasons, prevention experts have shied away from addressing the topic in the developed world, despite the fact that HIV testing is considered an essential ingredient in the prevention mix in developing world countries. However, at the 13th Conference on Retroviruses and Opportunistic Infections (CROI), held February 5-8, 2006, in Denver, it was clear that this issue can no longer be avoided by virtue of its controversial nature.

Universal Testing Recommended by CDC

A contentious issue in the world of HIV is whether -- given that, once tested, HIV-positive people do in general have less unsafe sex -- a drive for universal HIV testing is a way forward in the field of HIV prevention.

Two symposium contributions at this year's CROI exposed this as a very live issue, especially in the United States. In one presentation, Tom Coates (University of California, San Francisco) looked largely at drives to normalize HIV testing in Africa, and contrasted Africans' general agreement with normalizing HIV testing -- 82% of Botswanans, for instance, think that the routine HIV testing introduced in 2004 by Botswana's President, Festus Mogae, was a good thing -- with their individual distress at contemplating a positive result. In a qualitative survey, one said: "I have a dream of having children; if I test positive my dream will be shattered." Another said: "My father will chase me away from the house and call me 'Satan.'"

Timothy Mastro (US Centers for Disease Control and Prevention [CDC], Atlanta) got a considerably rougher ride from conference delegates, and session chair Jeffrey Klausner (San Francisco Department of Public Health) extended the question-and-answer session after Mastro's presentation, saying that "It's not often we get the most prominent members of the CDC in one room to answer these questions."

Mastro said that a CDC study showed that HIV-positive patients reduced the amount of unprotected serodiscordant sex they had by 68% after diagnosis.1 This led researchers to believe that the 25% of people who did not know their HIV status in the United States accounted for about 50% of HIV infections.

He cited the startlingly high prevalence and incidence figures among gay men, and particularly African-American gay men, in cities other than San Francisco. In a large sample of gay men in five US cities, 25% of gay men had HIV and 48% were unaware of their infection; 46% of African-American gay men were HIV-positive and 67% did not know about their HIV infection. Late testing was also common: 45% of AIDS diagnoses were among people who had been diagnosed less than 12 months previously.

Mastro said that HIV testing in the United States had not been increasing in recent years, despite the fact that the CDC had launched its "Advancing HIV Prevention" strategy in 2003, which aims to make voluntary HIV testing a routine part of medical care. He said that only about one in 500 visits to hospital emergency rooms involved an HIV test; a concern given that, when tested, rates of previously undiagnosed HIV among patients varied from 1.3% to 3.2%.

In Dallas, which adopted opt-out HIV testing in its sexually transmitted infections (STI) clinics in 1997, the proportion of patients tested for HIV increased from 78% to 97% in one year, and the number of positive tests had gone up 60% from 168 to 268. Mastro showed a notice from a Dallas STI clinic announcing that, "All patients seen in this clinic will be tested for gonorrhea, syphilis, chlamydia, and HIV."

Mastro added that before opt-out testing had been adopted in pregnant women in the United Kingdom, only 35% had chosen to be tested because they feared it indicated high-risk behavior, whereas 88% accepted opt-out testing. "We think the need for extensive pre-test counseling is less because it [is] 2006 and people now have a high level of knowledge about HIV," he said.

After two studies published in the New England Journal of Medicine last year found that routine screening would also be cost-effective, the CDC decided to revise its HIV screening guidelines to recommend routine, voluntary screening for all individuals aged 13 to 64 in health care settings, not based on risk, and annual HIV testing for people with risk behavior. Pre-test counseling would not be required. Health care settings include all hospital in- and out-patient clinics, as well as community clinics and STI clinics. An exception would be made for prisons, where it was recognised that receiving an HIV diagnosis created profound difficulties both for inmate and institution.

Mastro was bombarded with a battery of questions after his presentation. Among them were:

  • How would the CDC move from recommendation to implementation? The CDC had recommended names-based reporting years ago, but states did not move toward implementation until they were threatened with the removal of federal funds.

  • If the information given in pre-test counseling and discussion around informed consent is removed, where are patients going to get any opportunity to talk about HIV and harm reduction?

  • How real is the voluntary nature of the testing when the photo he showed of the Dallas notice indicated all patients would be tested for STIs, including HIV?

  • How is the opting-out process to work and how will it be recorded? Without adequate recording, patients could say they were tested without consent.


Matt Golden (University of Washington, Seattle) looked at a controversial prevention intervention adopted by gay men: serosorting.2 He defined the intervention as "the practice of preferentially choosing sex partners, or deciding not to use condoms with selected partners, based on their disclosed, concordant HIV status."

Five studies conducted from 1992 to 2005 found that gay men were between 2.5 and 9.1 times more likely to have unprotected anal intercourse with partners they knew were of the same HIV status as themselves than with partners of differing HIV status.

Data from Golden's own clinic found that HIV-positive patients were particularly likely to serosort. Forty percent and 49 percent of his HIV-positive patients, respectively, had unprotected receptive and insertive sex with HIV-positive partners but only 3% and 6%, respectively, with HIV-negative partners.

In his HIV-negative patients, 31% and 37%, respectively, had unprotected receptive and insertive sex with HIV-negative partners, and 19% and 15%, respectively, had unprotected receptive and insertive sex with HIV-positive partners -- less, though still a surprisingly high figure.

"Where the whole system breaks down," Golden commented, "is where the other partner is of unknown status." Here partners were almost equally likely to have unprotected insertive sex regardless of whether their own or their partner's status was unknown. In the case of receptive sex, there was some evidence that HIV-positive gay men were attempting to adopt "strategic positioning." HIV-positive men were somewhat more likely (31% versus 24%) to have unprotected receptive rather than insertive sex with partners of unknown status; conversely HIV-negative men were somewhat less likely (16% versus 22%).

Golden did not say whether any of these differences reached statistical significance. Golden then investigated whether serosorting was actually reducing the number of serodiscordant partners that gay men had, regardless of condom use. The answer was yes. In a population such as Seattle's, where 15% of gay men have HIV (not dissimilar to London), if gay men chose partners completely at random, and if they all had the mean number of partners rather than a few having many and many having a few, you would expect 54% of gay men to have at least one serodiscordant relationship per year (with the figure obviously lower for people with few partners and higher for those with many).

In fact about 35% of gay men had had at least one serodiscordant partner, so serosorting appeared to be reducing the number of serodiscordant relationships by about 40%, though Golden also suggested some of this was due to the fact that gay men tend to have sex with men fairly near their own age, and that because young men are less likely to have HIV than older men, some of this concordance was purely due to age similarity. Golden also found that between 13% and 18% of gay men were exclusive serosorters (i.e., only had unprotected sex with seroconcordant partners).

Is serosorting actually protective? When it comes to HIV-negative men, Golden found that the rate of new HIV diagnosis among patients who had unprotected sex but tried to do it only with same-status partners (2.6%) was intermediate between men who had unprotected sex regardless (4.1%) and men who attempted always to use condoms (1.5%). Adjusting for the number of partners, whereas condom use was 76% effective in preventing new HIV infections, serosorting was about 40% effective.

As a control, Golden also looked at the rate of STIs. In this case, as could be expected, there was no difference in the STI rates between serosorters and non-serosorters.

Was serosorting increasing? Golden showed data from London and San Francisco that suggested the proportion of unprotected sex that was discordant, especially as practiced by HIV-positive men, was decreasing, but said he had not seen the same pattern in Seattle.

Susan Buchbinder (San Francisco Department of Public Health) commented that the latest assessment from her city's health department was that, based on a number of key indicators in a number of studies, there was no decline in seroincidence among gay men. However, she added that these data did not preclude the possibility that serosorting could drive down infection rates.

Editor's Note: Reprinted with permission from Look to the March 2006 issue of the IAPAC Monthly for Mark Mascolini's comprehensive coverage of the 13th Conference on Retroviruses and Opportunistic Infections.


  1. Mastro T. Normalizing HIV testing in healthcare settings. 13th Conference on Retroviruses and Opportunistic Infections. February 5-8, 2006. Denver. [Abstract 164]

  2. Golden M. HIV serosorting among men who have sex with men: Implications for prevention. 13th Conference on Retroviruses and Opportunistic Infections. February 5-8, 2006. Denver. [Abstract 163]

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This article was provided by International Association of Physicians in AIDS Care. It is a part of the publication IAPAC Monthly.