HIV rate could be higher in black Americans because of less sexual mixing

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Researchers from the San Francisco Department of Public Health have published findings that, they say, support the idea that HIV prevalence may be higher in African-American (black) gay men because they are less likely to have partners of a different ethnic origin than other gay men.

As a result, black gay men tend to pick partners from a smaller available ‘pool’ and this may concentrate HIV infection within the community.

In a community survey of 1142 gay men in San Francisco, black gay men and men who have sex with men (MSM) were three times more likely to pick black partners than would be expected if partner selection was entirely independent of partner ethnicity. In turn white, Asian and Latino gay men were less likely to pick black partners than men of other races (though white men were also less likely to pick Latino partners).



Studies aim to give information that will be applicable to a large group of people (e.g. adults with diagnosed HIV in the UK). Because it is impractical to conduct a study with such a large group, only a sub-group (a sample) takes part in a study. This isn’t a problem as long as the characteristics of the sample are similar to those of the wider group (e.g. in terms of age, gender, CD4 count and years since diagnosis).

equivalence trial

A clinical trial which aims to demonstrate that a new treatment is no better or worse than an existing treatment. While the two drugs may have similar results in terms of virological response, the new drug may have fewer side-effects, be cheaper or have other advantages. 


When the estimate from a study differs systematically from the true state of affairs because of a feature of the design or conduct of the study.

risky behaviour

In HIV, refers to any behaviour or action that increases an individual’s probability of acquiring or transmitting HIV, such as having unprotected sex, having multiple partners or sharing drug injection equipment.

Ryan White HIV/AIDS Program

In the United States, the largest federally funded programme providing HIV-related services to low-income, uninsured, and underinsured people with HIV/AIDS.

Previous studies have found it hard to explain why the prevalence of HIV is so much higher among black gay men in the USA than in other racial groups. Black men are three times more likely to have HIV than gay men in general and 59% of new diagnoses of HIV among young men (under 24) were in black men in the years 2000 to 2004. Yet risk behaviour – in terms of number of partners and unprotected sex – has, if anything, been found to be lower than average in black gay men (see Millett and Harawa).

This led some researchers to hypothesise that the higher prevalence in black men might be a network effect. The current researchers hypothesised “that there might be less choice in sexual partners for black MSM, subsequently creating more closely knit sexual networks than other groups.” More tightly knit networks with frequent sexual interconnections can create conditions for the rapid spread of HIV and is one theory behind the high HIV prevalence in parts of Africa.

One previous survey by the same team in San Francisco (Berry et al.) found that black men had higher rates of same-ethnicity sexual partnerships and that they also mixed ages more: they were more likely to have partners ten or more years older than themselves, compared with other gay men. Generation-mixing, between older men and younger women, is another factor hypothesised to lie behind the African epidemic.

In the present survey, the same team of researchers explored reasons why this might be so.

They asked 1142 gay men about their own ethnicity and the number and ethnicity of their sexual partners in the previous six months. They also asked about the ethnicity of the men’s friends as well as their sexual partners, the preferred ethnicity of their sexual partners, the perceived ‘riskiness’ of men of different ethnicities in terms of their likelihood of passing on HIV, and whether they found it easy or difficult to meet partners of different ethnicities.

Of the sample, 56% were white, 21% Latino, 14% Asian and 9% black. The average number of partners in the previous six months was three, and this did not differ significantly between ethnic groups.

Half the white men, and the large majority of the other men (‘men of colour’) had had partners from a different ethnic group in the last six months. But black men were 300% more likely to have had black partners than would be the case if sexual partner choice had nothing to do with race. In contrast, Asian and white men were only 20% more likely, and Latino men 20% less likely, to have sex with men of their own racial background than would be predicted by random mixing.

In turn, white men were 34% less likely, Latino men 65% less likely, and Asian men 74% less likely to have had a black partner than if choice was random.

There was also a racial bias in who men said their partners were. While black men were 26% less likely to say they had had a non-black partner than would have been expected with random mixing, non-black men were 35% less likely to say they had had a black partner.

Respondents were asked a series of questions about the preferred ethnicity of sexual partners. Non-black men were significantly less likely to prefer black men as partners. Black men were significantly more likely to prefer Latino men as partners to men from any other ethnic group – even to other black men. Similarly, non-black men reported fewer black friends than friends from other ethnic groups and said that black men were more difficult to meet. Black men were perceived as a higher HIV risk by all groups.

The researchers stressed that exclusively choosing partners of one’s own ethnicity was not the most common behaviour. Half of all white men, despite being in the majority, had had a partner of another ethnicity in the previous six months and only 7.3% of non-white men had exclusively had relationships with men of their own ethnic background.

The researchers comment: “While the numbers of intraracial [i.e. same-race] partnerships of Black MSM appear modestly raised from 8.6% expected to 29% observed, this three-fold effect may serve to intensify the interconnections within this minority population relative to other MSM populations enough to accelerate the spread of HIV to the appreciable degree witnessed.”

However the researchers emphasised that the gay men they interviewed were more likely to have had sexual partners from a different ethnic background than would be found in an equivalent sample of heterosexuals. Overall, 46% of partnerships observed were interracial; in contrast, an estimated 7% of heterosexual marriages in the USA are interracial.

“We do not believe our data should be bluntly interpreted as evidence of racism among MSM,” they say. “Rather, we do interpret that our data capture less overt, more subtle factors stemming from the history and legacy of racism towards Blacks and segregation of Blacks in the US.”


Raymond HF and McFarland W Racial mixing and HIV risk among men who have sex with men. AIDS and Behaviour, online publication. DOI 10.1007/s10461-009-9574-6, May 2009.

Millett GA et al. Explaining disparities in HIV infection among black and white men who have sex with men: A meta-analysis of HIV risk behaviors. AIDS 21:2083–2091, 2007.

Harawa NT et al. Associations of race/ethnicity with HIV prevalence and HIV-related behaviours among young men who have sex with men in 7 urban centers in the United States. JAIDS 35:526–536, 2004.

Berry M et al. Same race and older partner selection may explain higher HIV prevalence among black men who have sex with men. AIDS 21:2349-50, 2007.