Centers for Disease Control and Prevention


CDC Transmission Study Puts Hispanic MSM at Leading Edge of HIV Spread


CDC Transmission Study Puts Hispanic MSM at Leading Edge of HIV Spread
9th IAS Conference on HIV Science (IAS 2017), July 23-26, 2017, Paris

Mark Mascolini

Analysis of more than 30,000 HIV sequences from across the United States yielded evidence that HIV is spreading rapidly in Hispanic men who have sex with men (MSM), particularly Hispanic MSM under 30 years old [1]. The findings suggest Hispanic MSM represent "the leading edge of HIV transmission" in the country.

Estimated HIV transmission across the United States stands at about 4 transmissions per 100 person-years, according to CDC researchers who conducted the new study. But transmission rates probably exceed that estimate in certain populations. The CDC team conducted this analysis to home in on the leading edge of HIV's spread by identifying and characterizing molecular clusters with recent rapid growth.

The study involved HIV-1 polymerase sequences from 30,323 people diagnosed with HIV from 2013 through 2015 in 27 jurisdictions across the United States. To identify transmission clusters, the researchers calculated genetic distance for each pair of sequences using a pairwise threshold of 0.005 substitutions per site. They defined a rapidly growing transmission cluster as one with 5 or more transmissions during 2015. The team performed molecular clock phylogenetic analysis "to estimate time to most recent common ancestor and internal node ages, which we used as a proxy for transmission events."

This analysis turned up 13 rapidly growing clusters involving a median of 17 HIV transmissions (range 6 to 22). There were 196 people in these clusters, including 41% diagnosed in 2015 and 63% with recent infection. Molecular clock phylogenetic analysis determined that cluster age ranged from 1.8 to 9.2 years. Of 182 total transmissions, 23 (13%) occurred within 1 year.

Calculating transmission rate as number of transmissions in the cluster divided by total HIV-infected person time, the CDC team determined a transmission rate of 35 per 100 person-years in the 13 rapidly growing clusters. This rate exceeds the overall estimated US HIV transmission rate (4 per 100) by almost 9 times.

Next the investigators compared the 196 people in the 13 rapidly growing clusters with the 30,127 other people who contributed a sequence to the analysis. The rapid-cluster group included significantly higher proportions of 6 groups:

-- MSM (94% versus 62% of all others, P < 0.001)
-- Hispanic/Latino (49% versus 28%, P < 0.001)
-- Age under 30 at diagnosis (68% versus 41%, P < 0.001)
-- Under-30 MSM (63% versus 31%, P < 0.001)
-- Under-30 Hispanic/Latino MSM (32% versus 9%, P < 0.001)
-- Drug resistance-associated mutations (43% versus 20%, P = 0.006)

Blacks were significantly less likely to be in one of the 13 clusters (14% versus 40%, P = 0.001).

The CDC concluded that the rapidly growing clusters "likely reflect the leading edge of HIV transmission" in the United States, "where rapid transmission results in a disproportionate number of new HIV infections." The investigators called for enhanced prevention efforts targeting Hispanic MSM.


  1. Oster AM, France AM, Panneer N, et al. Analysis of U.S. HIV sequence data indicates that recent and rapid HIV transmission is focused among young Hispanic/Latino men who have sex with men. 9th IAS Conference on HIV Science (IAS 2017), July 23-26, 2017, Paris. Abstract WEPDX0103.