Sexual Risk Trajectories Among MSM: Implications for PrEP
Sexual Risk Trajectories Among MSM: Implications for PrEP
Our analysis of longitudinal data from the MACS demonstrates that HIV-negative MSM exhibit relatively stable yet distinct patterns of SRB over time. More than half of our sample rarely engaged in high-risk behaviors (low-risk group: 63.0%) over the 8-year study period. However, 22.9% of participants (moderate-risk group) occasionally practiced high-risk behaviors, whereas 14.1% of participants (high-risk group) engaged in such behaviors with greater frequency and duration.
Given the high probability of engaging in SRBs among members of the high-risk group and that 32.2% of participants in that group seroconverted during the study period, HIV-negative MSM similar to those following a high-risk trajectory in our sample would likely benefit most from PrEP use. Although most members of the high-risk group were not at constant risk, over 90% of participants following a high-risk trajectory exhibited continuous risk periods with an average duration of ~2 years. These findings suggest high-risk MSM transition between low-risk periods and high-risk periods or "seasons of risk" over time. Thus, a targeted approach to PrEP delivery among MSM during "seasons of risk" may be more beneficial than continuous or prolonged PrEP use among high-risk MSM.
Our findings also indicate that MSM following distinct sexual risk trajectories can be distinguished by certain individual-level characteristics. Many of the characteristics associated with following a high-risk trajectory (ie, young age, distress or depression, and substance use) have previously been identified as proximal predictors of SRBs among MSM. However, to our knowledge, this is the first study to examine and demonstrate a relationship between these characteristics and longitudinal patterns of risk among HIV-negative MSM. Thus, our findings provide an understanding of the length of time MSM at ongoing high-risk may remain at risk and how such MSM can be identified, and therefore are particularly relevant to the development of more targeted PrEP delivery guidelines based on the Centers for Disease Control and Prevention's current recommendation that PrEP be offered to MSM "at substantial, ongoing, high-risk for acquiring HIV infection."
Younger age, being White, and earning an annual income ≥$20,000 at the index visit were associated with membership in both the moderate- and high-risk trajectory groups. Young MSM (<30 years of age) are at greatest risk of HIV infection in the United States and engage in UAI more frequently than older MSM; thus, young MSM are often the focus of HIV prevention efforts. However, given that 61.0% of participants in the high-risk group were at least 30 years old at the index visit, our findings suggest that high-risk periods occur well beyond 30 years of age among MSM. Incorporating and retaining young MSM in HIV prevention programs that include targeted PrEP delivery could potentially reduce their risk of HIV acquisition over a number of years.
Despite the fact that Black MSM are disproportionately affected by HIV/AIDS and are at greatest risk of HIV infection in the United States, we found that being non-White was associated with membership in the low-risk group. Previous studies have shown that high-risk behaviors are practiced with the same or lower frequency among Black MSM compared to other MSM and suggest that sexual network characteristics among Black MSM may explain racial disparities in the risk of HIV infection. Although we used a comprehensive SRB score in our analysis, our score does not account for sexual network characteristics, such as age or race mixing, which may be needed to accurately describe risk among non-White MSM.
Both distress or depression symptoms and reported substance use at the index visit were associated with following a high-risk trajectory but not a moderate-risk trajectory. Although distress or depression symptoms and reported substance use may be ongoing for individuals who follow high-risk trajectories, our findings suggest that reports of these factors even at a single point in time are predictive of long-term patterns of risk. Assessing recent or current distress or depression and substance use may aid clinicians in the identification of MSM who exhibit "seasons of risk" for potential PrEP use.
Our study has several limitations. Although we restricted our sample to younger and more racially/ethnically diverse MACS participants, those included in our sample are still older and less diverse than those at greatest risk of HIV infection in the United States. MACS participants also represent a highly motivated group of MSM who have been retained in a cohort study for a number of years and thus may differ from MSM in general. The increasing proportion of participants reporting no AI over time may be explained by the fact that MSM engage in AI less frequently with age, but could also have been due to poorer retention rates among those at greatest risk. Although MACS participants still active at the index visit did not differ from those who were inactive on SRBs (ie, the number of reported sexual partners), they did differ on a number of demographic characteristics, thus different sexual risk trajectories may have been identified within the full sample. Furthermore, there is some suggestion that group-based trajectory modeling has a tendency to over-extract trajectory groups within populations. However, Nagin and Tremblay argue that trajectory groups should be thought of as an approximation to a continuous distribution of individual-level trajectories within populations and cautions against the interpretation of identified groups as truly distinct entities. Thus, group-based trajectory modeling is useful for describing individuals with similar trajectories along a continuum. Moreover, despite the fact that participants were assigned to the group for which they had the highest posterior probability of membership, trajectory group assignments are not certain. However, the majority of HIV seroconversions occurred among members of the high-risk group suggesting that participants were appropriately assigned according to risk. Additionally, because we assumed that 6-month intervals with missing data were no or low-risk intervals, we may have underestimated the true frequency and duration of risk within our sample. Furthermore, although we created a comprehensive SRB score based on data presented by Vallabhaneni et al, we cannot be certain of the accuracy of our score in classifying risk. Previous research also suggests that partner type (main vs. casual) is strongly associated with condom use during AI among MSM. However, MACS behavioral questionnaires do not collect the partner type for reported AI partners; thus, our score is further limited by the fact that we cannot account for differences in risk by partner type. Finally, despite the fact that audio computer-assisted self-interviewing was implemented at most MACS sites, social desirability bias may have led to underreporting of SRBs, and hence an underestimation of the associated risks particularly in the high-risk group.
Despite these limitations, the large sample of HIV-negative MSM from across the United States, long duration of follow-up, and use of a comprehensive SRB score are some of the many strengths of our study. Our findings expand the current understanding of SRBs among MSM and should be considered in the development of targeted PrEP delivery guidelines for similar MSM populations. Such guidelines could enable clinicians to efficiently screen and identify MSM who exhibit "seasons of risk" for potential PrEP use. However, to ensure PrEP coverage throughout an individual's duration of risk, future research should investigate factors associated with the transition from low-risk to high-risk periods among high-risk MSM.
Discussion
Our analysis of longitudinal data from the MACS demonstrates that HIV-negative MSM exhibit relatively stable yet distinct patterns of SRB over time. More than half of our sample rarely engaged in high-risk behaviors (low-risk group: 63.0%) over the 8-year study period. However, 22.9% of participants (moderate-risk group) occasionally practiced high-risk behaviors, whereas 14.1% of participants (high-risk group) engaged in such behaviors with greater frequency and duration.
Given the high probability of engaging in SRBs among members of the high-risk group and that 32.2% of participants in that group seroconverted during the study period, HIV-negative MSM similar to those following a high-risk trajectory in our sample would likely benefit most from PrEP use. Although most members of the high-risk group were not at constant risk, over 90% of participants following a high-risk trajectory exhibited continuous risk periods with an average duration of ~2 years. These findings suggest high-risk MSM transition between low-risk periods and high-risk periods or "seasons of risk" over time. Thus, a targeted approach to PrEP delivery among MSM during "seasons of risk" may be more beneficial than continuous or prolonged PrEP use among high-risk MSM.
Our findings also indicate that MSM following distinct sexual risk trajectories can be distinguished by certain individual-level characteristics. Many of the characteristics associated with following a high-risk trajectory (ie, young age, distress or depression, and substance use) have previously been identified as proximal predictors of SRBs among MSM. However, to our knowledge, this is the first study to examine and demonstrate a relationship between these characteristics and longitudinal patterns of risk among HIV-negative MSM. Thus, our findings provide an understanding of the length of time MSM at ongoing high-risk may remain at risk and how such MSM can be identified, and therefore are particularly relevant to the development of more targeted PrEP delivery guidelines based on the Centers for Disease Control and Prevention's current recommendation that PrEP be offered to MSM "at substantial, ongoing, high-risk for acquiring HIV infection."
Younger age, being White, and earning an annual income ≥$20,000 at the index visit were associated with membership in both the moderate- and high-risk trajectory groups. Young MSM (<30 years of age) are at greatest risk of HIV infection in the United States and engage in UAI more frequently than older MSM; thus, young MSM are often the focus of HIV prevention efforts. However, given that 61.0% of participants in the high-risk group were at least 30 years old at the index visit, our findings suggest that high-risk periods occur well beyond 30 years of age among MSM. Incorporating and retaining young MSM in HIV prevention programs that include targeted PrEP delivery could potentially reduce their risk of HIV acquisition over a number of years.
Despite the fact that Black MSM are disproportionately affected by HIV/AIDS and are at greatest risk of HIV infection in the United States, we found that being non-White was associated with membership in the low-risk group. Previous studies have shown that high-risk behaviors are practiced with the same or lower frequency among Black MSM compared to other MSM and suggest that sexual network characteristics among Black MSM may explain racial disparities in the risk of HIV infection. Although we used a comprehensive SRB score in our analysis, our score does not account for sexual network characteristics, such as age or race mixing, which may be needed to accurately describe risk among non-White MSM.
Both distress or depression symptoms and reported substance use at the index visit were associated with following a high-risk trajectory but not a moderate-risk trajectory. Although distress or depression symptoms and reported substance use may be ongoing for individuals who follow high-risk trajectories, our findings suggest that reports of these factors even at a single point in time are predictive of long-term patterns of risk. Assessing recent or current distress or depression and substance use may aid clinicians in the identification of MSM who exhibit "seasons of risk" for potential PrEP use.
Our study has several limitations. Although we restricted our sample to younger and more racially/ethnically diverse MACS participants, those included in our sample are still older and less diverse than those at greatest risk of HIV infection in the United States. MACS participants also represent a highly motivated group of MSM who have been retained in a cohort study for a number of years and thus may differ from MSM in general. The increasing proportion of participants reporting no AI over time may be explained by the fact that MSM engage in AI less frequently with age, but could also have been due to poorer retention rates among those at greatest risk. Although MACS participants still active at the index visit did not differ from those who were inactive on SRBs (ie, the number of reported sexual partners), they did differ on a number of demographic characteristics, thus different sexual risk trajectories may have been identified within the full sample. Furthermore, there is some suggestion that group-based trajectory modeling has a tendency to over-extract trajectory groups within populations. However, Nagin and Tremblay argue that trajectory groups should be thought of as an approximation to a continuous distribution of individual-level trajectories within populations and cautions against the interpretation of identified groups as truly distinct entities. Thus, group-based trajectory modeling is useful for describing individuals with similar trajectories along a continuum. Moreover, despite the fact that participants were assigned to the group for which they had the highest posterior probability of membership, trajectory group assignments are not certain. However, the majority of HIV seroconversions occurred among members of the high-risk group suggesting that participants were appropriately assigned according to risk. Additionally, because we assumed that 6-month intervals with missing data were no or low-risk intervals, we may have underestimated the true frequency and duration of risk within our sample. Furthermore, although we created a comprehensive SRB score based on data presented by Vallabhaneni et al, we cannot be certain of the accuracy of our score in classifying risk. Previous research also suggests that partner type (main vs. casual) is strongly associated with condom use during AI among MSM. However, MACS behavioral questionnaires do not collect the partner type for reported AI partners; thus, our score is further limited by the fact that we cannot account for differences in risk by partner type. Finally, despite the fact that audio computer-assisted self-interviewing was implemented at most MACS sites, social desirability bias may have led to underreporting of SRBs, and hence an underestimation of the associated risks particularly in the high-risk group.
Despite these limitations, the large sample of HIV-negative MSM from across the United States, long duration of follow-up, and use of a comprehensive SRB score are some of the many strengths of our study. Our findings expand the current understanding of SRBs among MSM and should be considered in the development of targeted PrEP delivery guidelines for similar MSM populations. Such guidelines could enable clinicians to efficiently screen and identify MSM who exhibit "seasons of risk" for potential PrEP use. However, to ensure PrEP coverage throughout an individual's duration of risk, future research should investigate factors associated with the transition from low-risk to high-risk periods among high-risk MSM.
