Social and network factors may explain higher HIV infection rates for black men who have sex with men in the US

Young black gay and bisexual men are more likely to be exposed to HIV than their white or Hispanic peers even though they have fewer sex partners overall and have less condomless anal sex, a study from Chicago has found.

Dr Brian Mustanski and colleagues at Northwestern University found three factors that explained why the HIV infection rate is so much higher in black gay men than other racial groups.

Firstly black men were more likely to have HIV and, if they did have HIV, three times more likely to have a detectable viral load and so be infectious.

Secondly, black men were more likely to have certain psychological factors that are strongly associated with HIV infection, especially having experienced stigma and childhood sexual abuse.

Thirdly, black men’s sexual networks were constructed in a way that made repeat exposures to HIV more likely. They were more likely to restrict sexual contacts to other black men and women. Although they were less likely to share sexual partners with other friends, they were more likely to have sex, often repeated, with individual members of their friendship network.

Several studies have found that risk behaviour alone fails to account for the racial disparities seen in HIV infection among men who have sex with men (MSM). In 2015, black MSM accounted for 41% of all HIV-positive MSM in the US. If this trend persists, half of all black MSM will become infected with HIV in their lifetime.

The study

This cohort study with young men who have sex with men (YMSM) in Chicago explored the effects of networks on HIV transmission in order to explain the racial disparities in HIV rates among MSM in the US. As well as individual factors, the authors took a network approach, involving measures of sexual connectedness within networks which could possibly account for higher HIV rates among black YMSM. Factors such as homophily (the likelihood of having a same-race sexual partner) and density of networks may play a crucial role in HIV transmission.

Researchers used community sampling, drawing on partner and peer connections when recruiting participants. All of the 1015 participants were aged 16-29, with 34% identifying as black, 30% as Latino, 25% as white and 11% as other. Of the cohort, 49% indicated some college education, with a higher percentage of white MSM indicating this (59%).

A higher percentage of black MSM indicated bisexuality as a sexual preference when compared with white MSM (26% vs 10%). There was a much larger percentage of HIV-positive black MSM (32%) than either Latino (13%) or white MSM (2%) in the cohort.

Networks were generated by asking each participant to indicate individuals who were known to them socially, sexually or as people they took drugs with. Once the participant named five network members, information was gathered regarding demographics, characteristics of the relationship and interactions between the participant and the network members. For sexual partners, detailed information was obtained, including frequency of sexual contact, condom use and so forth.

Sexual connectedness within a network was measured by measuring three attributes:

• Homophily: the degree of sexual preference you have for people of your own ‘type’ (in this case, race).
• Transitivity: the average number of sex ties between network members.
• Density: the ratio of sex ties between members in a network out of all the possible sex ties that could exist.

Black MSM were found to have high levels of density and racial homophily, but low transitivity. In other words, black men were more likely to have sex only with men and women of their own race than white men; they were more likely to have sex with more of the people they did know; but they were less likely to have sex with people who also had sex with each other.

Black MSM also reported a larger number of sexual partners who were female, transgender or did not identify as gay.

At the individual level, results show that there were racial differences in terms of substance abuse and psychological symptoms: black men were more likely to use cannabis, with white men significantly more likely to report alcohol abuse. Depression scores were significantly higher for white MSM than for black MSM, whereas suicide attempts were more common among black MSM than white MSM.

There were significant racial differences in risk-taking behaviour, with black MSM reporting the lowest number of sexual partners and engaging in less condomless sex. Black MSM reported experiencing significantly higher stigma (both externalised and internalised) than either white or Latino MSM.

Biologically, in addition to higher HIV rates, and more likelihood of detectable viral loads among HIV-positive black MSM (61% vs 20% for white MSM), higher rates of rectal STIs were also observed in black men.

At a structural level, for those who were HIV positive, there were no racial differences regarding the number of missed antiretroviral doses and number of visits to healthcare practitioners. However, the authors did not comment on health insurance differences between racial groups or the proportion of black HIV-positive men on treatment. Additionally, there were only five HIV-positive white men in the study – this small sample may not reveal significant structural differences between the racial groups.

Despite higher HIV infection rates, black YMSM reported more lifetime HIV tests. There were no differences observed among the racial groups when looking at pre-exposure prophylaxis (PrEP) use in the last six months. Black YMSM reported significantly more violence and trauma with childhood sexual abuse experienced by 32% compared to 14% for young white MSM.

These results indicate important multilevel differences that may account for racial disparities in HIV infection rates. The network findings suggest that black YMSM are exposed to HIV infection via fewer pathways but engage in more sexual contact with other network members. Thus, even though the total number of partnerships may be lower, the high density creates more opportunity for HIV exposure from repeat encounters.

This research emphasises the importance of interventions that directly address social determinants such as stigma and victimisation, while also accounting for network trends. Future interventions may have greater success at reducing racial infection disparities by addressing not only individual level factors, but also working at the structural and network levels to prevent infection.