Britt Skaathun’s study is based on data from uConnect, a cohort study which recruited black MSM aged 16 to 29 who were living in south Chicago.
Each participant was asked to recruit a number of friends or peers who were also eligible for the study, according to a methodology known as respondent-driven sampling. It is often used to help researchers engage populations that might be otherwise hard to reach. In this case, it has also helped them map part of each man’s social and sexual network. The researchers say that young black MSM’s networks are dynamic, with social connections frequently becoming sexual connections and vice versa.
Data from 457 participants were analysed. They had an average age of 23 and 39% were already living with HIV. While 66% identified as gay, 27% identified as bisexual and 4% as straight (all had recently had sex with a man). Half had health care coverage, a third were unemployed, a quarter had been homeless in the past year, and just under half had ever been involved with the criminal justice system.
Looking at each man’s social networks (of up to 7 other study participants), the researchers found that:
- 46% of men had a social network in which all members were HIV negative
- 10% had a social network in which less than half of members were HIV positive
- 44% had a social network in which more than half of members were HIV positive.
To assess ‘network viral load’, the researchers calculated the proportion of each man’s social network that was viremic, in other words with a viral load above 20,000 copies/ml. Take, for example, a man who had social connections with five other study participants. If two of these peers were HIV negative, one was HIV positive with an undetectable viral load, and two were HIV positive with high viral loads, then 40% of his social network would be viremic.
Looking at the data:
- 46% of men had a social network in which all members were HIV negative
- 37% had a social network in which fewer than 10% were viremic
- 17% had a social network in which more than 10% were viremic.
Moreover, network viral load was associated with having HIV. After adjusting for other factors which could influence the results (such as sexual behaviour, drug use, age and education), men with a social network in which more than 10% of members were viremic were three times more likely to be HIV positive (adjusted odds ratio 2.75) than men with an HIV-negative network. Similarly, men with a social network in which fewer than 10% were viremic were twice as likely to be HIV positive (adjusted odds ratio 1.85). The ‘community viral load’ of the area in which a man lived was not associated with his HIV status.
However, those results are cross-sectional, from one point in time only. More persuasive would be longitudinal results, if they demonstrated that men with a high network viral load at the beginning of the study were more likely to acquire HIV later on.
A separate analysis of the same uConnect dataset does show links between men’s social networks and their own risk of seroconversion. From Ethan Morgan and colleagues at the University of Chicago, it is also published online ahead of print in the Journal of Acquired Immune Deficiency Syndromes.
Morgan had follow-up data from 343 young black MSM who were HIV negative when they enrolled in the study; 33 of them (10%) seroconverted during the 18 months of follow-up. This analysis considered the number of men in their social network who had either acquired HIV in the previous nine months or had long-term HIV infection. During recent infection, people have exceptionally high viral loads which make HIV transmission more likely.
Looking at the social networks the participants described when they entered the study, having more recently infected contacts was associated with a greater risk of seroconversion. After adjusting for other factors that could influence the result, each additional recently infected social contact multiplied the risk of seroconversion by 13 (adjusted odds ratio 12.96).
On the other hand, the number of network members with long-term HIV infection (who are more likely to be taking treatment) made no difference to men’s risk of acquiring HIV.
For each additional social contact who was HIV negative, the risk of seroconversion was lowered (adjusted odds ratio 0.14). And having more PrEP users in one’s social network also lowered the risk (adjusted odds ratio 0.44).