The Impact of Age and Race on New HIV Infections Among Men Who Have Sex with Men (MSM) in Los Angeles County (LAC), 2008-2010

BACKGROUND:  Compared with the national HIV epidemic, a greater proportion of HIV diagnoses in Los Angeles County (LAC) occur in MSM, including MSM who use injection drugs (MSM/IDU) (55% vs. 85%, respectively).  Recent national HIV incidence estimates showed that Black MSM ages 13-29 years were most at risk of acquiring new HIV infections.  We estimated HIV incidence by age and racial/ethnic groups to better understand the role of age in the risk of HIV infection for White, Black and Latino MSM in LAC.

METHODS:  We used data from the HIV Incidence Surveillance system in LAC to estimate the number of new HIV infections among MSM, including MSM/IDU, during 2008-2010.  HIV Incidence Surveillance relies on the Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS) methodology, which uses the BED HIV-1 capture enzyme immunoassay, to identify recent HIV infections by testing remnant diagnostic serum. This population-based incidence method uses HIV testing data from newly diagnosed cases and imputes testing history and BED results for persons who are unaware of infection. The proportion of MSM in LAC was estimated to be 8.2% of the male population (Lieb, 2011).  This percentage was applied to California State Department of Finance population estimates.

RESULTS:  We estimate that 3,247 MSM ages 18-39 years were infected with HIV (27% were Black, 47% Latino and 20% White).  In comparison, the percentage of 18-39-year-old MSM residents in LAC were 8%, 24%, and 52%, respectively, by race/ethnicity.  Across all age groups, the proportion of new infections among Black MSM exceeded their distribution in the population (Table 1).  Notably, we estimate 9% of new infections were among 18-24-year-old Black MSM while they compose only 3% of 18-24- year-old MSM residents in LAC.                      

CONCLUSIONS:  While it is common practice to present HIV surveillance data in broad age categories, this analysis demonstrates that providing data in more narrow age groups presents a clearer picture of those most at risk for new HIV infections.  Comparing proportions of Black MSM residents in LAC to those estimated to have become HIV infected, Black MSM were disproportionately impacted by new HIV infection.  This finding was especially evident among the 18-24 year olds where the proportion of HIV-infected Black MSM exceeded their proportion in the LAC population compared with White and Latino MSM.  While this racial/ethnic disparity decreased with age, Black MSM remained the most heavily impacted across all ages between 18 and 39 years.