Poster presentation at the 9th annual Canadian Conference on HIV/AIDS Research, in April 2000, in Montreal.

Longitudinal patterns of numbers of male and female sexual partners in a cohort of HIV-negative gay and bisexual men (1995-98)

Kevin JP Craib, Kathy Li, Keith Chan, Mary Lou Miller, Steve Martindale, Martin T. Schechter, Robert S. Hogg.

Objective: To describe longitudinal patterns of annual numbers of sexual partners in a cohort of homosexual and bisexual men in Vancouver.

Methods: The Vanguard Project (VP) is an ongoing prospective study of gay and bisexual men aged, living in the Greater Vancouver region. Since May 1995, VP participants have completed self-administered questionnaires and undergone HIV testing on an annual basis. We studied HIV-negative participants who completed their baseline questionnaire during 5/95-4/96, and who completed at least one annual follow-up visit during the periods 9/96-10/97 and 9/97-11/98. Data regarding socio-demographic characteristics and self-reported annual numbers of male and female sexual partners in the previous year were obtained. Male sexual partners were defined as regular (at least one sexual encounter per month) and casual (less than one sexual encounter per month) partners.

Results: A total of 308 HIV- men were studied. Of these, 244 (79%) completed at least one follow-up questionnaire. Demographic characteristics at baseline: median age = 26 years (range 18-31); 78% were Caucasian; 91% had completed high school; 25% had annual income below $10,000; 27% were unemployed; and 14% lived in unstable housing. Men who completed follow-up questionnaires reported higher annual incomes, less unemployment, and more stable housing. The perecentage of men who reported having one or more female sexual partners significantly decreased from 16% at baseline to 4% at both follow-up questionnaires. The percentages of men reporting one or more regular male sexual partners in the previous year were 24%, 18%, and 20%, respectively. Percentages reporting 2 or more casual male sexual partners in the previous year were 68%, 64% and 66%, respectively.

Conclusions: Our data indicate there is a relatively high stability in the number of male sexual partners reported. However, the decrease in female sexual partners likely reflects loss to follow-up patterns within the cohort, or an actual decreasing trend.

To describe longitudinal patterns of annual numbers of sexual partners, frequency of unprotected anal sex and patterns of substance use among young HIV-negative gay and bisexual men enrolled in an open cohort.

The Vanguard Project

The Vanguard Project is a prospective study of HIV incidence and risk behaviours among young men who have sex with men. Eligible participants are between the ages of 15 and 30 at baseline, living in the Greater Vancouver area, who have not previously tested HIV-positive. Since the study began in May 1995, over 850 participants have completed self-administered questionnaires and undergone HIV testing on an annual basis.

Study design

Eligible participants for this particular analysis were HIV-negative participants who completed a baseline questionnaire between May 1995 and April 1996, and who completed at least one follow-up questionnaire during one of three time periods:

• September 1996 to October 1997;
• September 1997 to October 1998; and
• September 1998 to October 1999.

For the purpose of this analysis, self-reported data were examined including demographic characteristics, numbers of male and female sexual partners in the previous year, frequency of unprotected anal sex, and substance use.

Male sexual partners were defined as either regular (at least one sexual encounter per month) or casual (< once/month).

We identified 308 men who fit the criteria for this analysis.

Demographic characteristics

The majority of these participants were Caucasian (74%), employed (73%) and living in stable housing (86%).

80% had completed high school and 75% reported annual incomes above $10,000.

Median age was 26 years (range: 18-31).

Numbers of FEMALE sexual partners

At the baseline visit, 48 participants (16%) reported having sex with one or more female partners in the previous year.

During the latter three time periods, less than 5% of participants reported sexual contact with women.

Numbers of MALE sexual partners

Throughout the four time periods, over 90% of participants had sex with one or more male partners in the previous year.

Over the four time periods, 85%, 79%, 76% and 78% of participants had more than one partner in the previous year.

Numbers of REGULAR male sexual partners

Throughout the four time periods, over 70% of participants had sex with one or more regular male partners in the previous year.

Over the four time periods, 52%, 43%, 35% and 37% of those with regular partners had more than one regular partner.

Numbers of CASUAL male sexual partners

Throughout the four time periods, over 70% of participants had sex with one or more casual male partners in the previous year.

Over the four time periods, 93%, 89%, 91% and 83% of those with casual partners had more than one casual partner. In each time period, approximately 60% of these men reported having sex with two to 19 casual partners.

Substance use (Table 1)

With a few exceptions, substance use patterns remained very stable over the entire observation period, with alcohol, cannabis and tobacco being the most commonly-used drugs.

The use of tobacco, LSD and heroin decreased over time, likely reflecting patterns of attrition within the cohort.

Unprotected anal sex (Table 2)

Levels of unprotected anal sex remained fairly stable over the entire observation period. Throughout the four time periods, approximately 35% of participants had unprotected anal sex with regular partners and 15% did so with casual partners.

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Reasons for not using condoms (Tables 3 & 4)

Throughout the four time periods, the most common reasons cited for not using condoms for anal sex with regular partners were involvement in a long-term and/or monogamous relationship, a desire for increased intimacy, and the assumption that both partners were HIV-negative.

Among men with casual partners, the assumption that both partners were HIV-negative still figured prominently, along with getting "carried away," being intoxicated and not caring at the time as the most common reasons given for not using condoms for anal sex.

For both regular and casual partners, other common reasons related to increased comfort and pleasure.

Annual numbers of male sexual partners reported by HIV-negative Vanguard participants have remained highly stable over the course of the study, from mid-1995 to the end of 1999. The decline in the annual numbers of female sexual partners likely reflects loss to follow-up patterns within the cohort, as hard-to-reach street-involved participants were more likely to report sex with both men and women at baseline.

Patterns of substance use remained stable over time, with the exception of tobacco, certain street drugs and injection drugs, which can also be attributed to patterns of attrition within the cohort.

Many young gay and bisexual men who engage in unprotected anal sex appear to be practising a form of "negotiated safety": they are far more likely to dispense with condoms with regular partners than with casual partners; and although the reasons for having unprotected anal sex differ between regular and casual relationships, in both cases one of the most common reasons cited was the assumption that both partners were HIV-negative.

The authors gratefully acknowledge the staff, participants and Community Advisory Board of the Vanguard Project; participating doctors and HIV testing clinics; and the

National Health Research Development Program, Health Canada, for project funding. Poster designed by Steve Martindale.