In the United States, young men who have sex with men (YMSM), particularly black/African American (black) or Hispanic/Latino YMSM, bear a disproportionate burden of HIV infections. HIV transmission among YMSM has been found to be highly assortative by race but disassortative by age. We examined temporal trends in transmission for subgroups of YMSM (MSM aged 13-24 years).
We analyzed HIV-1 pol sequences reported to the National HIV Surveillance System for all MSM aged ≥13 years who had HIV diagnosed during 2006–2013 and were from 26 jurisdictions. We identified potential transmission pairs at a genetic distance threshold of ≤1.5% and constructed transmission networks using HIV-TRACE. For YMSM, we determined race/ethnicity and age of potential transmission partners. Assuming HIV was acquired from only one person, we assigned partners of YMSM with >1 transmission partner a weight equal to the inverse of the number of partners. We constructed two multivariable logistic regression models and calculated prevalence ratios (PRs) and 95% confidence intervals (CIs) to examine the change from 2006–2009 to 2010–2013 in the proportion of potential transmission partners 1) of the same race/ethnicity and 2) at least 5 years older, for each subgroup of YMSM, adjusting for geography and transmission category.
Of 7,867 YMSM with a potential transmission partner, 67% had partners of the same race/ethnicity and 36% had partners >5 years older. Transmission among blacks remained highly assortative by race, with approximately 80% of blacks linking to other blacks. Assortativity by race/ethnicity among Hispanics/Latinos increased over time, with substantial increases seen in MSM aged 13-19 years (from 46% to 59%, PR=1.34, CI=1.10–1.64). Although a higher proportion of white YMSM had older transmission partners (48%) compared with blacks (30%) and Hispanics/Latinos (42%), the proportion of older transmission partners increased over time for all racial/ethnic groups, with the most substantial increases among blacks and Hispanics/Latinos aged 13-19 years (black: PR=1.42, CI=1.23–1.65; Hispanic/Latino: PR=1.31, CI=1.05–1.64).
These data provide evidence for continued transmission among networks of black YMSM and expansion of transmission among networks of Hispanic/Latino YMSM. Additionally, YMSM are increasingly linked to older partners. Prevention programs aimed at reducing incidence among YMSM may be strengthened by also ensuring that older MSM are virally suppressed.