Science Spotlight

HIV prevention: unique considerations for transgender populations

Table showing the numbers of individual needed to detect a 35-70% effect size.

A recent publication from Dr. James Hughes and colleagues from the Vaccine and Infectious Disease Division and the Public Health Sciences Division at Fred Hutch reviews the issues related to designing and conducting HIV-prevention studies on transgender populations. Improving HIV-prevention efforts in these populations is important as several studies have shown that transgender individuals, especially transgender women, are at a high risk of HIV infection. The review was published in the August issue of the Journal of Acquired Immunodeficiency Syndromes.

The paper addresses a number of topics, specifically: sampling, recruitment and retention, sample size, and prevention by intervention on HIV-negative and positive individuals. The paper identifies social stigma and the consequent high rate of unemployment, homelessness and alcoholism as some of the causes of high risk of HIV infection. Moreover, there are difficulties in recruiting and retaining subjects in HIV-prevention studies a challenge that may be overcome by the establishment of a trust-based relationship between the study subjects and the investigators. Sampling associated challenges are another issue discussed in the review. Convenient recruitment methods for transgender studies, such as word-of-mouth or venue-based recruitment, are useful for randomized placebo-controlled trials, where the effect of an intervention is internally controlled. Instead, to estimate absolute population characteristics, a more unbiased method is required. One possible approach is to limit the number of recruitments of a single subject, to expand the recruited population. Another important consideration for studies in these populations is relative to the sample size. In fact, even though the prevalence of HIV-infection in transgender populations is high, the sample size would still be high, as shown in the Table due to low retention rate. Moreover, since the risk of acquiring HIV is related to specific group behavior and cultural characteristics, a study should involve multiple sites to better mirror the complexity of the real situation.

All these issues have limited the number of studies on either HIV-negative or HIV-positive transgender populations. One exception is the inclusion of a small group of HIV-negative transgender men and women in a pre-exposure prophylaxis (PrEP) trial. PrEP consists in the administration of antiretroviral drugs for prevention, and has been shown effective in cis-gender men and women (although less consistently). In transgender subjects participating in the trial, no differences in HIV infection rates were observed between PrEP and placebo. This could be the result of low adherence to the tested drugs or to a biological/immunological difference as well as to pharmacological interactions with other drugs, such as hormones. Another prevention strategy is to reduce viral loads of positive subjects, which requires increased testing, linkage to care and adherence to antiretrovirals. Previous studies assessed the efficacy of different strategies to intervene at different steps of the care cascade, but none of them specifically addressed the transgender population.

Now that different preventive methods have been proven efficacious in cisgender subjects, it is definitely time to evaluate them in transgender populations, designing studies that take into account specific features of such populations, with the review published by Dr. Hughes being a guide for them.


Hughes JP, Emel L, Hanscom B, Zangeneh S. 2016. Design Issues in Transgender Studies. J Acquir Immune Defic Syndr, 72 Suppl 3, S248-51.