Some clients may see these numbers and think their risk of HIV transmission is low. Therefore, caution is needed when interpreting them. If these numbers are provided to clients, they should be accompanied by information that helps shed light on why the risk may be higher than it seems. Transmission can occur after one exposure. It is important to emphasize that a person could become infected from having unprotected sex once or a person could have unprotected sex many times and not become infected, regardless of how low or high the risk per exposure is.
It does not mean that a person needs to be exposed times for HIV infection to occur. These are estimates of average risk in the absence of biological factors that increase risk. They are averages and do not represent the risk from all exposures to HIV through a certain type of sex.
We know that no two exposures to HIV are exactly the same. Research shows that, in addition to the type of sex that led to the exposure, several factors can increase or decrease the risk that an exposure to HIV leads to infection.
These include the presence of sexually transmitted infections STIs , a high viral load, a man being uncircumcised, a woman menstruating, other bleeding and activities that can cause tearing and inflammation, such as rough sex, longer sex, douching, enemas before anal sex, and tooth brushing, flossing or dental work before oral sex.
Each exposure to HIV carries a unique risk of transmission that depends on the type of sex and a combination of biological factors. The risk of HIV transmission may be much higher than these averages if biological risk factors are present. For example, research shows that STIs and some vaginal conditions, such as bacterial vaginosis, can increase the risk of HIV transmission by up to 8 times. We also know that for every fold increase in viral load, the risk of HIV transmission increases by 2 to 3 times.
The more exposures, the greater the risk. Although the risk of HIV transmission from a single exposure may seem low to some people, this risk increases over multiple exposures. In other words, a person who is exposed to HIV more often has a greater overall risk of HIV transmission than someone who is exposed less often. Differences in risk Information on how risky certain types of unprotected sex are compared to others may help people make more informed decisions about the type of sex they are having.
Based on the meta-analysis estimates, we can draw several conclusions: Receptive anal sex carries a much higher risk of HIV infection than receptive vaginal sex. Receptive anal sex is riskier than insertive anal sex.
Research suggests the risk of HIV transmission from receptive anal sex is 3 to 23 times higher than from insertive anal sex. Receptive vaginal sex is riskier than insertive vaginal sex. The risk from receptive vaginal sex is about twice as high as that from insertive vaginal sex.
It is unclear exactly how much less risky oral sex is compared to vaginal and anal sex. It's important to provide clients with additional information to help them interpret the findings. Here are some key messages: These numbers are challenging to calculate and should therefore be considered rough estimates do not represent the risk of transmission from all exposures to HIV represent the average risk of transmission in the absence of biological factors that can increase risk such as STIs and a high viral load are most relevant to people in stable monogamous serodiscordant relationships These numbers may seem low but HIV transmission can occur after a single exposure the risk may be much higher if certain biological risk factors, such as STIs or a high viral load, are present as more exposures to HIV occur, the overall risk of transmission increases most HIV transmissions in Canada occur through unprotected anal and vaginal sex There are several ways of reducing the risk of HIV transmission from an exposure, such as post-exposure prophylaxis PEP , using antiretroviral treatment to reduce viral load , circumcision, treatment for STIs and vaginal conditions, or engaging in lower-risk activities.
There is no way to reduce the risk of HIV transmission to zero after an exposure occurs. Taking measures to avoid an exposure in the first place for example, through the correct use of condoms or other barrier methods, or by ensuring a partner has the same HIV status can help reduce the overall risk of HIV transmission.
HIV transmission risk through anal intercourse: International Journal of Epidemiology. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. American Journal of Epidemiology. Heterosexual risk of HIV-1 infection per sexual act: Systematic review of orogenital HIV-1 transmission probabilities. Contribution of sexually transmitted infections to the sexual transmission of HIV.
Bacterial vaginosis and HIV acquisition: Bacterial vaginosis associated with increased risk of female-to-male HIV-1 transmission: Journal of Infectious Diseases.
HIV-1 transmission, by stage of infection. James has an undergraduate degree in Microbiology and Immunology from the University of British Columbia.