For the first time in a decade, the Centers for Disease Control and Prevention (CDC) has conducted a major scientific review of HIV prevalence as well as risk factors for the virus in the transgender population. Additionally, the agency has provided the first such estimates specific to transgender men.

Previous estimates, including a 2008 CDC study, indicated that perhaps 25 to 28 percent of transgender individuals in the United States are living with HIV. The new CDC paper, a systematic review and meta-analysis published in the American Journal of Public Health in December, arrived at much lower prevalence estimates, indicating that 18.8 percent of trans women and 2 percent of trans men.

Nevertheless, these figures remain alarmingly high for trans women in particular, indicating the need for efforts to mitigate HIV risk and promote testing of and treatment for the virus among trans individuals.

The authors of the new paper searched for studies published between 2006 and 2017 that provided data on the HIV status of transgender participants who identified as either trans women or trans men. The researchers acknowledged that many trans and gender-nonconforming individuals identify as neither male nor female but stated that their paper focused on the two most common trans identities.

They came up with 88 studies, which were conducted between 2001 and 2015. Half of them were published between 2014 and 2017. Fifty-four percent were considered high-quality sources of information. Fifty-two percent were conducted in San Francisco, New York City, Los Angeles or Boston.

Ninety-two percent of the studies recruited transgender people either by what is known as convenience sampling, in which participants are recruited at places where they are more likely to be found, or snowball sampling, in which early participants help recruit further participants.

Neither sampling method provides a representative sample of the transgender population, so the study authors cautioned that their findings may not provide an accurate depiction of HIV prevalence and risk factors among trans individuals. In fact, because convenience and snowball sampling may favor those with a higher risk for HIV—because, for example, such individuals are more likely to frequent locations where the sampling was conducted—the study may have overestimated the prevalence of the virus in this population.

That said, the fact that more trans people have entered such research studies in recent years may have helped provide a more comprehensive look at the population and also may help explain why the new paper’s HIV prevalence estimate is considerably lower than previous estimates.

Sixty-six percent of the studies reported data on HIV prevalence for either trans men or women, 8 percent did so for both groups and 13 percent provided only overall estimates for transgender participants. The study groups ranged between 8 and 7,454 people, including groups of 8 to 2,136 trans women, 16 to 528 trans men and 31 to 7,454 trans people in which the study did not break down the cohorts according to gender.

Sixteen percent of the studies included participants younger than 18 years old. Seventy-seven percent included participant groups in which a majority was nonwhite.

Based on the data in these studies, the CDC researchers estimated that 13.7 percent of transgender individuals in the United States are HIV positive, including 18.8 percent of trans women and 2 percent of trans men.

These estimates were based on the fact that 9.2 percent of the trans study participants had HIV according to laboratory testing, including 14.2 percent of trans women and 3.2 percent of trans men. Among the trans women, 44.2 percent of the African American, 25.8 percent of the Latinas, 9.8 percent of those in the “other” race category and 6.7 of the whites were living with the virus. There were not enough data about trans men to similarly parse the statistics according to race for this group.

A high rate of 72.8 percent reported HIV testing. Just under half (48.6 percent) said they were aware of Truvada (tenofovir disoproxil fumarate/emtricitabine) as pre-exposure prophylaxis (PrEP), a rate the study authors considered concerningly low and cause for stepping up the promotion of the HIV prevention method among trans individuals. They also suggested promoting condoms in this population.

Looking at the prevalence of various behaviors associated with a higher risk for HIV, the researchers found that 31 percent of the participants reported a history of sex work, including 37.9 percent of the trans women and 13.1 percent of the trans men. Citing a 2013 paper, the investigators noted that among trans women, such transactional sex “can play an economic role or affirm a desired sense of femininity.” Consequently, they advised that employment and vocational interventions could benefit this group.

Overall, 38.2 percent of the participants reported engaging in condomless sex; 36.4 percent said they had sex while drunk or high; 20 percent reported sex with partners who were HIV positive or of an unknown HIV status; and 41.7 percent reported having sex with multiple partners during a recent period, with an overall average of four partners. These rates did not greatly differ between trans women and men.

The investigators theorized that the lower HIV rate among trans men compared with trans women may have been driven by lower rates of risky sexual behaviors among the trans men as well as by their tendency to have cisgender female partners (who have a lower HIV rate than cisgender men who have sex with trans women).

As for drug and alcohol use, which is also associated with HIV risk, 10 percent of all participants reported injecting illicit drugs, a figure the researchers considered low. A total of 37.4 percent of the trans women reported injecting hormones or body fillers or enhancers; there weren’t enough data about the use of such injections among trans men. Promisingly, just 2.5 percent of all participants reported sharing needles for any form of injection.

A total of 47.5 percent and 39.6 percent of trans women and men reported drinking alcohol; a respective 36 percent and 38.1 percent reported noninjection drug use.

“For the transgender population, drug or alcohol use might be a coping mechanism in response to gender-related discrimination and gender-minority stress,” the researchers stated.

Hormone use was reported by 67.1 percent of trans women and 67.7 percent of trans men.

As for broader issues associated with HIV risk, 43.6 percent of trans women and 54.2 percent of trans men reported depression, and a respective 24.8 percent and 47.8 percent reported having attempted suicide. A total of 47.8 percent said they had been subject to mental or physical abuse and 39.8 percent reported experiencing sexual abuse. Gender-based discrimination had affected 47.8 percent of the participants, according to their reports. Homelessness or unstable housing was reported by 30.3 percent.

Just 39.2 percent of the trans women and 56.8 percent of the trans men reported being employed. A respective 71.9 percent and 70.1 percent had health insurance, compared with 90 percent of the general population. A total of 43.3 percent of the participants had a history of incarceration.

“Exploring trans men’s sexual behavior in relation to the gender of the sexual partner and the challenges specific to trans men regarding social constructs and expectations of masculinity are promising directions for research,” the study authors projected.

They also cautioned that the overall cohort of trans men they assembled for their paper may have underrepresented this demographic’s true HIV prevalence across the U.S. population because their analyses suggested they were missing studies that included groups of trans men who had a high rate of the virus.

The study authors concluded that their overall findings “indicate that transgender persons experience multiple and overlapping health, social and economic vulnerabilities that increase their HIV risk. Addressing these contextual factors warrants multicomponent interventions that recognize and address these vulnerabilities and their intersections. Structural interventions such as anti-stigma mass-media campaigns and antidiscrimination laws in employment and housing might be necessary components of a comprehensive approach for reducing HIV vulnerability for transgender persons and communities.”

Health care providers, the CDC researchers stressed, “can play a pivotal role” in addressing HIV-related disparities in the transgender population by offering prevention services as a component of trans-specific health care.