Abstract
Near 60% of new HIV infections in the United Kingdom are estimated to occur in men who have sex with men (MSM). Age-disassortative partnerships in MSM have been suggested to spread the HIV epidemics in many Western developed countries and to contribute to ethnic disparities in infection rates. Understanding these mixing patterns in transmission can help to determine which groups are at a greater risk and guide public health interventions. We analyzed combined epidemiological data and viral sequences from MSM diagnosed with HIV at the national level. We applied a phylodynamic source attribution model to infer patterns of transmission between groups of patients. From pair probabilities of transmission between 14,603 MSM patients, we found that potential transmitters of HIV subtype B were on average 8 months older than recipients. We also found a moderate overall assortativity of transmission by ethnic group and a stronger assortativity by region. Our findings suggest that there is only a modest net flow of transmissions from older to young MSM in subtype B epidemics and that young MSM, both for Black or White groups, are more likely to be infected by one another than expected in a sexual network with random mixing.
Highlights
M en who have sex with men (MSM) account for40% of new HIV diagnoses in Europe.[1]
We used a phylodynamic inference based on sequences collected among diagnosed
By modeling an epidemic process that is compatible with the evolution of transmitted viruses and epidemiological surveillance data, we characterized past transmission events among nearly 15,000 men who have sex with men (MSM) patients at the national level
Summary
Kingdom (UK), nearly 60% of new infections are estimated to occur in MSM, there is a recent sign of decline in diagnoses recorded in London.[2] It has been estimated that the largest contribution to transmission in the UK is attributable to young HIV-positive MSM.[3] More generally, since the early work from Morris et al.,[4] young MSM having sex with older partners have been suggested to increase the risk of infection[5,6] and to represent a significant driver of the epidemic in North America.[7] This disassortative age mixing pattern is considered in interaction with mixing by ethnicity.[8,9] Among MSM, black men appear to be more affected by HIV in both the UK and US contexts and age mixing patterns have been evaluated to illuminate this ethnic disparity in prevalence.[10,11,12] In addition to the question of transmission patterns by age and ethnicity, it is unclear whether the geographic variation in diagnosis rate for MSM is solely reflecting the demographic distribution of groups at greater risk in the country, or can be explained by a varying extent of transmission between persons of different regions.[13] Assessing the primary sources of infection in these different demographic groups could prove helpful to design more effective intervention strategies
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