Clients often want to know how great their risk of becoming infected with HIV or transmitting HIV is and how effectively different strategies can reduce this risk. Answering these questions in a way that is meaningful to clients can be complex and challenging. Frontline HIV prevention workers need to have a solid understanding of risk and how to help clients assess their risk in order to prevent new HIV transmissions.
What Is Risk? How Can It Be Communicated? And Why Is It Important?
Risk tells us about the possibility of harm. In the context of HIV prevention, it refers to the chance that specific activities or actions will result in HIV transmission.
Risk can generally be communicated to clients in two ways:
- as a numerical expression. For example, the average risk of HIV transmission during one act of unprotected receptive anal sex is 1.4%; or antiretroviral treatment can reduce the risk of heterosexual HIV transmission by up to 96%.
- as a qualitative expression. For example, the risk of HIV transmission during unprotected receptive anal sex is "very high"; or antiretroviral treatment can be "highly effective" at reducing the risk of heterosexual HIV transmission.
Accurately assessing and communicating risk is important because a client's perceived risk of HIV transmission plays a major role in determining whether or not they will take measures to reduce their risk (by, for example, using condoms). Other factors that come into play when people make decisions about what precautions they will or will not take include how much they want to avoid HIV transmission and how much they feel unprotected sex increases their sense of pleasure and intimacy.
Risk and Its Many Shades of Grey
Risk is all about uncertainty. If a specific outcome is certain -- 0% or 100% -- then no risk is involved. People often feel comfortable with certainties but with risk there are none.
When it comes to HIV transmission, uncertainties are unavoidable. Completely eliminating one's risk of HIV transmission is not possible for many individuals because few sexual activities carry no risk of HIV transmission and few prevention strategies are 100% effective. At the same time, no activities carry a 100% chance of HIV transmission.
To complicate matters, people often have difficulty understanding probabilities and may interpret them in different ways. For example, "1.4%" or "high-risk" can mean different things to different people.
In addition, each individual has a different level of risk they are willing to take, which is often influenced by their attitudes and beliefs regarding risk, HIV and pleasure. Some people are more comfortable with a certain level of risk while others are more averse to taking risks.
Also, many factors and variables influence a person's risk of HIV transmission, including the viral load of the HIV-positive partner, the kind of sex they are having (anal, vaginal or oral), whether he or she is the insertive or receptive partner, whether either partner has a sexually transmitted infection (STI), and any tearing and inflammation at the mucous membranes. As a result, every client's risk of HIV transmission is unique. The more factors that are taken into account, the more accurate the risk estimate will be. Unfortunately, we don't always know how much each one impacts a person's overall risk of HIV transmission. Consequently, measures of risk tend to be generalizations and are always "best guesses."
A Tale of Two Risks: Absolute and Relative
Clients generally want to know two things about their risk:
- their risk of becoming infected with HIV or transmitting HIV (also known as their absolute risk); and
- how much a risk factor or prevention strategy can change their risk (also known as relative risk).
Exploring Absolute Risk
Absolute risk can refer to risk from one specific exposure or it can refer to the risk of transmission over a given period of time.
Risk From a Single Act
Because the risk of HIV transmission from an act of unprotected sex depends on a wide range of factors, it is difficult to estimate and assess someone's individual risk. Some researchers have managed to estimate the average risk of HIV transmission from an exposure to HIV through specific types of sex.2 For example, the average risk of HIV transmission through one act of unprotected receptive anal sex with a person who is HIV-positive has been estimated to be 1.4%.
It is not easy for a person to use these numbers to assess their personal risk. It's important to keep in mind that regardless of how low a percentage may seem, transmission can occur after a single exposure to HIV. Also, these numbers do not represent the risk from all exposures to HIV; they represent the average risk of HIV transmission in the absence of biological factors (such as other STIs and a high viral load) that can increase risk.
Many frontline service providers and transmission guidelines use qualitative expressions, such as "high-risk" or "low-risk," to describe the level of risk associated with different activities. For example, the HIV Transmission Guidelines for Assessing Risk published by the Canadian AIDS Society (CAS) assign activities to one of four categories (no risk, negligible risk, low risk or high risk) based on two criteria: whether there is a potential risk of transmission and whether there is evidence of transmission. Qualitative expressions can be easier to communicate than numerical expressions and may reflect the risk of HIV transmission in a way that is more meaningful to the client.
However, the use of qualitative expressions has its disadvantages:
- Expressions such as "high-risk" and "low-risk" can be open to interpretation unless the criteria used to assign an activity to a category are clearly explained.
- These expressions don't tell a client how high or low the risk is.
- Grouping multiple activities into a single risk category may not reflect some of the important differences in risk between activities within a category. For example, all types of unprotected anal and vaginal sex are normally considered high-risk activities but research shows that unprotected receptive anal sex carries a higher risk of HIV transmission than other types of unprotected vaginal and anal sex.
- This approach focuses on the activity that led to the exposure and often ignores biological factors, such as viral load, that can significantly increase or decrease the risk of HIV transmission. For example, clients may want to know if unprotected vaginal and anal sex are still high-risk activities when the viral load is undetectable.
Discussing with clients the absolute risk from an exposure to HIV may help them assess their risk and adopt strategies to reduce it (such as using condoms, lubrication, engaging in less risky types of sex, reducing their -- or their partner's -- viral load, treating STIs, or using post-exposure prophylaxis.)
Risk Over Time
Similar to the risk of HIV transmission from a specific exposure, the risk over a given period of time is also unique to each individual. This risk depends on how many times a person is exposed to HIV -- which, in turn, depends on how often a person is having sex, the chances that their partner(s) have a different HIV status than them, how consistently and correctly they are using condoms -- and the unique transmission risk from each exposure that does occur.
In HIV prevention, risk assessments tend to focus on a client's risk from a single exposure to HIV and not their risk over time. This may lead people to underestimate their risk because risks that may be considered small in the short term can accumulate and became large in the long term. In other words, a client's overall probability of HIV transmission increases the more they are exposed to HIV (a concept known as cumulative risk).
For example, the average risk of HIV transmission from one act of unprotected vaginal sex is estimated to be 0.1%. Although a client may consider this risk to be low, this risk will grow if they continue to have unprotected vaginal sex. After 100 exposures through unprotected vaginal sex, the cumulative risk of HIV transmission becomes approximately 10%. This risk could be even higher if certain biological risk factors are present, for example, if one partner has an STI or if the HIV-positive partner has a high viral load.
Exploring Relative Risk
Relative risk tells us about how much something, such as a risk factor or prevention strategy, can change a client's risk. For example, acute HIV infection can increase the risk of HIV transmission by up to 2500% (a 26-fold increase);4 STIs and some vaginal conditions, such as bacterial vaginosis, can increase the risk of transmission by up to 700% (an 8-fold increase);5-7 or being on treatment and having an undetectable viral load can decrease the risk of heterosexual HIV transmission by up to 96% (a 26-fold decrease).8
Clients need to know about the factors that can increase or decrease their risk and by how much these factors can change their absolute risk.