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Research Letters

‘Serosorting’ in casual anal sex of HIV-negative gay men is noteworthy and is increasing in Sydney, Australia

Mao, Limina; Crawford, June Ma; Hospers, Harm Jc; Prestage, Garrett Pb; Grulich, Andrew Eb; Kaldor, John Mb; Kippax, Susan Ca

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doi: 10.1097/01.aids.0000226964.17966.75
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The practice of ‘serosorting’ by men who have sex with men (MSM) was defined by Suarez and colleagues [1,2] as ‘discussing HIV status with potential partners and only engaging in risk behaviour with those they believe are of a similar serostatus’ [2]. HIV-positive MSM have been reported to engage in unprotected anal intercourse (UAI) with either steady (regular) or casual seroconcordant partners (‘positive–positive’ sex) [3–9]. Very few studies, however, have provided data on serosorting among HIV-negative MSM. One US study suggested that men who believed they were HIV negative could be increasingly avoiding HIV-positive sex partners [10].

In this paper we provide data on ‘serosorting’ in casual encounters from a cohort of confirmed HIV-negative gay men in Sydney [11]. Participants were not asked whether they actually engaged in serosorting. Rather, ‘serosorting’ was inferred on the basis of information collected on unprotected anal intercourse with casual partners (UAIC) who participants reported to be of the same serostatus as themselves, i.e. HIV negative.

We analysed data collected between 2002 and 2005 inclusive (interviews after July 2005 have not yet been included). For each year, we calculated the mean number of UAIC partners in the previous 6 months, stratified by partners’ reported HIV status (unknown, negative, or positive). In addition, for each year, the proportions of UAIC partners who were HIV negative, HIV positive, and HIV unknown were calculated. With year as the independent variable, we tested the significance of trend (over time) for the total number of UAIC partners as well as for the number of UAIC partners reported to be HIV negative (seroconcordant). We used general estimating equations in STATA 8.2 (STATA Corp., College Station, Texas, USA) and calculated per-year rate ratios (RR) and 95% confidence intervals (CI).

In the whole cohort, there was a decrease in the mean number of total UAIC partners in the 6 months before interview (RR per year 0.92, 95% CI 0.90–0.94, P < 0.001). However, when stratified by partner's HIV serostatus, there was an increase in the mean number of UAIC partners reported to be HIV negative (RR 1.11, 95% CI 1.05–1.17, P < 0.001). This corresponded to an increase in the proportion of HIV-negative UAIC partners: from 12.3% in 2002 to 24.3% in 2005 (Table 1).

Table 1
Table 1:
Mean number of unprotected anal intercourse with casual partners in the previous 6 months, by year and partners' HIV serostatus, 2002–2005, Health in Men cohort.

To verify that results from the whole cohort were not merely caused by a possible change in cohort composition, we then selected men who had completed all four interviews from 2002 to 2005 (N = 302). The pattern from the subsample was matched with that from the whole sample. There was a decrease in the mean number of total UAIC partners over the 4-year period (RR 0.89, 95% CI 0.86–0.92, P < 0.001) but a significant increase in the mean number of UAIC partners reported to be HIV negative (RR 1.31, 95% CI 1.19–1.45, P < 0.001). The proportion of HIV-negative UAIC partners increased from 6.4% in 2002 to 24.6% in 2005 (Table 1).

In general, we found a significant increase over time in apparent ‘serosorting’ in casual encounters among HIV-negative gay men in Sydney, where HIV testing rates are high and stable. Although the majority of UAIC (over 60%) still occurred with partners of an unknown HIV status, our results show that in 2005, ‘serosorting’ accounted for nearly one-quarter of all reported UAIC. This was even more pronounced against the background of a decrease in the total number of UAIC partners over time. More studies are needed to explore the meaning of UAIC within the context of negative seroconcordancy in different populations of MSM.

There are a number of limitations to our findings. We did not ask whether participants interpreted their practice as serosorting, rather evidence of ‘serosorting’ was inferred from information provided by respondents about their UAIC partners. Furthermore, our findings may be limited to men who have annual or frequent HIV tests, but this applies to the great majority of gay men in Australia.

For men who have not been diagnosed as HIV positive, ‘serosorting’ is based on the assumed serostatus of both self and casual partners. Such a practice, especially if used as a deliberate strategy to replace consistent condom use with casual partners, is highly problematical. First, even if both partners are, indeed, HIV-negative, unprotected anal intercourse still carries risks of other sexually transmitted infections, which can facilitate HIV transmission [12]. Second, the assumed HIV-negative status of self or of casual partners does not necessarily correspond with the actual HIV status as seroconversion may have occurred since the last HIV test. This particularly pertains to countries in which the level of HIV testing is low, regular HIV testing has not yet been widely adopted, or HIV incidence is high. Third, assuming that all casual sex partners will honestly disclose their HIV status is unrealistic. Serosorting in casual encounters is not the same as ‘negotiated safety’ [2,13]. Finally, the exchange of information about each other's assumed HIV status is often not practised through direct face-to-face verbal discussion but rather is implied or inferred from non-verbal cues [1,2,14], making it even more problematical than when such a discussion does occur. In this context, the perception of a casual partner's HIV status may also be related to certain degrees of familiarity between them.

Future research should investigate reasons for the increase in ‘serosorting’ among HIV-negative MSM, including the role of the Internet, as serosorting can be easily facilitated through the Internet [9,15–17]. Whether online HIV status disclosure is the main reason for this increase is worthy of examination.

Policy makers, educators and researchers in the HIV prevention field should be alerted to this phenomenon of HIV-negative ‘serosorting’ in casual sex, and investigate whether this is indeed a new trend. They need to address this issue in prevention messages to make gay and bisexual men aware of the risks of HIV-negative serosorting with casual partners. One way forward may be to ensure that education and prevention materials differentiate clearly the consequences of serosorting among HIV-positive men from those among HIV-negative men.


The authors would like to thank the Australian Federation of AIDS Organisations and the AIDS Council of New South Wales for collaboration with the project, and the men who have participated in the Health in Men study.

Sponsorship: Support was received from the Commonwealth Department of Health and Ageing (Canberra), the New South Wales Health Department (Sydney), and the US National Institutes of Health (National Institutes of Health/National Institute of Allergy and Infectious Diseases/Division of Acquired Immune Deficiency Syndrome: HIV Vaccine Design and Development Team award N01-AI-05395).


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© 2006 Lippincott Williams & Wilkins, Inc.