Recent scientific advances mean that we now have a better understanding of the underlying factors that can increase someone's risk of HIV infection. At the same time, we also have more effective interventions to prevent HIV transmission. Despite these advances, HIV transmissions in Canada are continuing at a high rate and certain populations remain disproportionately affected by the HIV epidemic. But even within these populations, we know that HIV risk is not evenly distributed. A complex range of interrelated and synergistic factors contribute to a higher vulnerability to HIV infection for some individuals. A more holistic and comprehensive approach to HIV is needed, but a major barrier to such an approach is the fragmentation of the diverse range of services needed to address HIV risk for individuals within these populations.
This article reviews our new understandings about HIV risk and prevention and explores how HIV prevention can be improved.
HIV in Canada
According to the latest estimates from the Public Health Agency of Canada (PHAC), there were 2,570 new HIV infections in Canada in 2014. The latest estimates also show that certain populations continue to be disproportionately affected by the HIV epidemic. These populations include gay men and other men who have sex with men (MSM), Aboriginal people, people who use injection drugs, and people from HIV-endemic countries. Additional research tells us that transgender people in Canada may also be disproportionality affected by HIV. According to the latest PHAC estimates, the rate of HIV infection among people from HIV-endemic countries is 6.3 times higher than the rate for other Canadians, and the rate among Aboriginal people is 2.7 times higher than the rate for non-Aboriginal Canadians. Estimates from 2011 indicate that MSM are 71 times more likely to get HIV than other men and people who use injection drugs are 46 times more likely to get HIV than people who do not.
But these numbers don't tell us the whole picture. HIV risk is not evenly distributed within these populations. Research tells us that many psychosocial factors occur unevenly across individuals within these groups and can combine synergistically to increase HIV risk. For example, in a study of gay, bisexual and other MSM in the U.S. it was found that the co-occurrence of four to five psychosocial factors (depression, alcohol use, stimulant use, polydrug use and childhood sexual abuse) created an 8.6-fold higher risk for HIV infection among men who experienced these factors over a four-year period compared to those who did not experience any of these factors. MSM with fewer psychosocial factors were also at higher HIV risk, but to a lesser extent. Canadian data also support that psychosocial factors syndemically impact vulnerability,, and that similar factors interact synergistically to increase HIV vulnerability in other populations, such as Aboriginal peoples.
Underlying Reasons for Increased HIV Risk
Factors that increase HIV vulnerability are diverse and complex. And, while these factors are inter-related and difficult to completely disentangle from each other, they are often distilled down into different categories, such as the biological, behavioural and psychosocial-structural.
At the most basic level, HIV transmission occurs from an exposure to HIV. However, not all exposures carry the same risk of HIV transmission and a range of biological factors can increase the HIV risk from an exposure. These factors include certain routes of exposure (for example, on average, receptive anal sex carries the highest risk of HIV transmission for the HIV-negative partner); the presence of a sexually transmitted infection (such as gonorrhea or syphilis) in either the HIV-negative or HIV-positive partner; the absence of post-exposure prophylaxis (PEP) or pre-exposure prophylaxis (PrEP) in the HIV-negative partner; and a higher viral load in the fluids of the HIV-positive partner.
In addition, there are a range of behavioural factors that can increase the chance that an exposure occurs in the first place (for example, a higher number of sexual or needle-sharing partners or lack of consistent condom use) or the chance that the exposure leads to HIV infection (such as lack of adherence to PEP or PrEP).
The psychosocial-structural factors that can increase HIV vulnerability include social determinants of health (SDOH) inequities and syndemic health issues. SDOH inequities include poverty, underemployment, illiteracy, underhousing, incarceration, and inadequate coping skills and social support networks. Many of these inequities are related to broader issues such as stigma, homophobia, racism and colonization, and poor access to education and health-related services. Syndemics refer to various co-occurring issues that can combine synergistically to increase HIV risk. These include substance use and addiction; anxiety, depression, and other mental health issues; and trauma, violence and abuse, including childhood abuse, sexual abuse, and intimate partner violence. Research shows that the more syndemic issues a person faces, the greater their risk for HIV infection.,,,
These three different types of factors that can increase HIV vulnerability (biological, behavioural, and psychosocial-structural) are strongly related. Inequities in the SDOH can exacerbate syndemic health issues, and SDOH inequities and syndemic issues can increase the prevalence of biological and behavioural HIV risk factors. For example, SDOH inequities and syndemic health issues can make it difficult for an individual to use, access, and adhere to an HIV prevention strategy. They can also make it difficult for people living with HIV to access HIV testing, care and support, and treatment services -- potentially resulting in a higher overall viral load in certain populations (also known as community viral load). A higher community viral load can increase the average risk from an exposure to HIV for people within that population or group. Higher rates of HIV infection within these populations can also create a higher prevalence of HIV (that is, more individuals with HIV in the community), increasing the chance that an exposure to HIV will occur (particularly within small sexual and injecting networks), thus further increasing HIV transmission risk. This may partially explain why some populations have a higher rate of HIV infection, but do not engage in a higher rate of behaviours that can lead to HIV infection.,, These examples highlight the overlap both within and between these three different types of factors that can increase HIV risk and that vulnerability to HIV goes beyond individual behaviours and choices.
The Need for Combination HIV Prevention
Our improved understanding of the underlying factors contributing to greater HIV vulnerability -- in addition to the expanding evidence base for HIV prevention and the emergence of new tools -- has broadened the range and depth of services and interventions which can now be considered relevant to HIV prevention. Some of these services are directly related to HIV (HIV risk-reduction counselling and PrEP, for example), while others may seem more distantly related (such as mental health and addiction services). Some interventions can be considered biomedical (such as PrEP and condoms), while others are behavioural (such as social marketing campaigns to improve condom use, medication-adherence counselling, and mental health counselling) or psychosocial-structural (such as improved access to PrEP, mental health services or supervised injection services). Some services can only be provided by physicians (PrEP, anti-depressants and methadone, for example), while others can be provided by a broader range of care providers (HIV risk-reduction and mental health counselling, for example).
The terms combination HIV prevention, comprehensive prevention and holistic prevention are not new, and are based on the idea that there is overlap and synergy between these different interventions and services. For example, the success of biomedical tools relies on behavioural and psychosocial-structural interventions to address an individual's needs in a holistic way and subsequently facilitate uptake, access, and consistent and correct use.
A significant barrier toward the adoption of a more comprehensive approach to HIV prevention is the fragmentation and siloization of the different services relevant to HIV prevention. Often, the diverse array of HIV-related services is not well integrated or connected and, as a consequence, there are missed opportunities to effectively address an individual's risk of HIV infection in a holistic way. For example, non-clinical and clinical services are often poorly linked, as are services that are directly and distantly related to HIV.
A research-based example that highlights the importance of a comprehensive approach -- and the potential negative impact of service fragmentation -- comes from PROJECT Explore, the largest ever behavioural HIV prevention intervention study among gay men in the United States. The PROJECT Explore intervention involved several one-on-one HIV risk-reduction counselling sessions, which were found to reduce the overall rate of HIV infection among men in the study by 18%. This risk reduction was small, and additional analyses suggested that the intervention had no effect for men with a history of childhood sexual abuse. Of concern, 40% of men in this study reported a history of childhood sexual abuse, and these men were also more likely to have depression and use street drugs and alcohol. The high overall prevalence of these health issues may explain the small overall reduction in HIV risk provided by the HIV risk-reduction counselling.
The PROJECT Explore example highlights the importance of better integrating services and using interactions with clients to screen them for syndemic health issues and SDOH inequities and, if appropriate, engaging them in additional services to address them. Once clients are engaged, strategies are needed to link and retain them across a continuum of relevant services, and ensure such interactions do not become missed opportunities to improve holistic health and reduce HIV vulnerability. There is also a need to ensure the needed services are available, are appropriate for the population being served, and are resilience-based.
Time for an HIV Prevention Cascade for People at Ongoing Risk for HIV Infection?
In recent years, the fragmentation of services relevant to the health and well-being of people living with HIV has received a significant amount of renewed attention. This can be seen in the recent focus on the HIV care cascade, which is a way of visualizing the engagement of people living with HIV in the services necessary to improve their health and reduce their risk of HIV transmission. These services include those to improve HIV testing, linkage to care, retention in care, HIV treatment initiation, and treatment adherence. The focus on this cascade has led to the development and evaluation of interventions to improve linkage across these services.
The disconnect between services aimed at improving health and reducing HIV risk for people at high ongoing risk of HIV infection is in need of similar renewed attention. Some organizations and agencies have begun to include a prevention component in their HIV care cascades, but little work has been devoted to the monitoring and evaluating of engagement in this cascade.