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Studies Shed Light on Sexual Transmission of HIV Among Young Gay Men

Young men who have sex with men tend to have higher HIV viral load compared with heterosexuals, contributing to a greater likelihood of transmission, according to a recent report. Another recent study offers more information on the risk of HIV transmission associated with specific sexual activities in the absence of antiretroviral treatment.

Data from the Centers for Disease Control and Prevention (CDC) have shown that gay and bisexual men -- especially young gay/bisexual men and gay men of color -- have the highest rates of new HIV infection. But the exact risk factors underlying this disparity are not fully understood.

Viral Load

As described in the January 2, 2014, advance edition of AIDS, Jonathan Ellen and colleagues with the Adolescent Medicine Trials Network for HIVAIDS Interventions looked at HIV viral load levels and CD4 T-cell counts among youth age 12-24 in 14 U.S. cities.

Baseline viral load and CD4 count data were collected anonymously from youth linked to HIV care between March 2010 and November 2011. Most (78%) were male and 68% identified as gay or bisexual. Out of 1409 youth with HIV, 852 had both viral load and CD4 count data available.

Results

• Among youth with complete data, 34% had CD4 counts of 350 cells/mm³ or less, 27% had 351-500 cells/mm³, and 39% had more than 500 cells/mm³.
• Youth whose HIV risk factor was sex between men had higher viral load (mean of approximately 125,000 copies/mL) compared with those whose risk factor was mother-to-child transmission or heterosexual contact (approximately 47,000 copies/mL).
• Young men had higher viral load (mean of approximately107,000 copies/mL) compared with young women (approximately48,000 copies/mL).
• 31% of study participants who reported sex between men had viral load greater than 50,000 copies/mL -- a highly infectious level -- compared with 20% of youth in the heterosexual risk category and 18% in the perinatal transmission category.
• Lower CD4 count was significantly associated with higher viral load.

"Most HIV-infected youth have CD4+ cell counts and viral load levels associated with high rates of sexual transmission," the study authors concluded. "Untreated, these youth may directly contribute to high rates of ongoing transmission. It is essential that any public health test-and-treat strategy place a strong emphasis on youth, particularly young MSM."

However, the researchers suggested that these findings might be attributable to young gay men being diagnosed closer to the time of infection, when viral load is typically high, while older adults and heterosexuals tend to be diagnosed later.

Risk per Sex Act

In the second study, described in the January 1, 2014, Journal of Acquired Immune Deficiency Syndromes, Hyman Scott, Susan Buchbinder, and colleagues from the University of California at San Francisco and San Francisco Department of Public Health explored possible explanations for disparities in HIV incidence, focusing on per contact risk of HIV infection in the early years of combination antiretroviral therapy (ART). This is useful because it captures data from a time before many people were on effective therapy that fully suppresses viral load, which dramatically lowers the risk of HIV transmission.

The researchers looked at pooled data from 3 longitudinal studies of initially HIV negative MSM (HIV Network for Prevention Trials Vaccine Preparedness Study, EXPLORE behavioral efficacy trial, and VAX004 vaccine efficacy trial). The analysis included study visits at which participants reported unprotected receptive anal intercourse, protected receptive anal intercourse, or unprotected insertive anal intercourse with an HIV positive partner, HIV negative partner, or partner of unknown serostatus.

Results

• The estimated per contact risk was highest for unprotected receptive anal sex with an HIV positive partner (0.73%).
• The next highest risk activity was unprotected receptive anal sex with a partner of unknown serostatus (0.49%).
• The estimated per contact risk was much lower for protected receptive anal sex (0.08%) and unprotected insertive anal sex (0.22%) with an HIV positive partner.
• Average per contact risk for unprotected receptive and insertive anal sex with an HIV positive partner was 0.14% to 0.34% higher among younger compared with older participants.
• Average per contact risk for unprotected insertive anal sex was 0.08% higher for Latino compared with white participants, but evidence for black MSM was inconclusive.
• Estimated per contact risk rose with an increasing number of sexual partners, use of methamphetamines or poppers, and history of other sexually transmitted infections.

Based on these findings, the authors concluded, "Susceptibility or partner factors may explain the higher HIV conversion risk for younger MSM, some MSM of color, and those reporting individual risk factors."

They noted that per contact risk estimates were similar during the pre-ART and early ART era, likely because during the early years of ART only a small proportion of HIV positive gay men were on suppressive treatment that substantially lowered transmission risk. According to recent CDC estimates, now about 80% of people with HIV know they are infected and about 30% have suppressed viral load.

"There are several possible explanations for the finding of higher per contact risks among young MSM," the researchers wrote. "One is that younger MSM are less able than older MSM to negotiate safer sex with partners. For example, younger MSM may not have the skills or knowledge to navigate other risk reduction strategies with HIV-positive partners (such as withdrawal before ejaculation), which may have a lower HIV risk."

"[O]lder MSM may also have older HIV-positive partners who are often engaged in care and have lower HIV viral loads compared with younger HIV-positive MSM," they added. "Finally, although there is evidence of increased biologic susceptibility for young women, there are no current studies to suggest a biological basis to explain these disparities for young MSM."

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References

JM Ellen, B Kapogiannis, JD Fortenberry, et al. (Adolescent Medicine Trials Network for HIVAIDS Interventions. HIV viral load levels and CD4+ cell counts of youth in 14 US cities. AIDS. January 2, 2014 (Epub).

HM Scott, E Vittinghoff, R Irvin, S Buchbinder, et al. Age, Race/Ethnicity, and Behavioral Risk Factors Associated With Per Contact Risk of HIV Infection Among Men Who Have Sex With Men in the United States. Journal of Acquired Immune Deficiency Syndromes 65(1):115-121. January 1, 2014.