Treatment and Viral Load: What Do We Know About Their Effect on HIV Transmission?
Key Messages for People Living With HIV and Their Sexual Partners
While the above questions about HIV transmission risk are difficult to answer, there are key messages we can give to both people living with HIV, and their partners, to help maximize the prevention benefit of treatment and lower their risk of HIV transmission.
Key messages for monogamous serodiscordant couples
- Don't assume that the viral load is undetectable once treatment is started. It normally takes a few months after starting treatment for the viral load to reach undetectable levels. Your viral load should be undetectable for at least 6 months to ensure the risk of HIV transmission is reduced as much as it can be.
- Getting regular viral load tests is the only way to make sure the viral load is undetectable and stays that way. If medications are missed or drug resistance develops, the viral load may no longer be undetectable. Wait until your next viral load test to be sure.
- Both partners should get tested regularly for STIs and, if diagnosed, seek treatment as soon as possible. The risk of HIV transmission may be higher when there is an STI in either partner.6
- The risk of HIV transmission when the viral load is undetectable may be higher for receptive anal sex. Generally speaking, insertive anal sex (topping) is lower risk than receptive anal sex (bottoming) for the HIV-negative partner.11,25 Therefore, for same-sex male couples, the risk of HIV transmission may be reduced if the HIV-positive partner is the bottom (takes the receptive role) during anal sex.
- Condoms are highly effective at reducing the risk of HIV transmission when used consistently and correctly. Using condoms (with condom-compatible lube) as often as possible -- particularly when the risk of HIV transmission may be elevated, such as when medications are missed or either partner is diagnosed with an STI -- will help reduce the overall risk of HIV transmission.
Additional considerations for people with casual sexual partners
Although the above key messages apply to people who are not in a monogamous serodiscordant relationship, additional factors need to be considered for those who are having sex with casual partners.
For example, there is generally a higher risk of STI transmission in this context because it is more difficult to know for certain if either partner has an STI. This is because these infections don't always produce symptoms and a person may have become infected with an STI since their last test. Since STIs may increase the risk of HIV transmission when the viral load is undetectable, consistent use of condoms and regular screening for STIs may be important to lower the risk of STI and HIV transmission. In the context of casual sex, it is also important that HIV-negative individuals do not assume a casual partner (of known or potential HIV-positive status) has an undetectable viral load.
Those who have casual partners -- and are also in a stable serodiscordant relationship that is "open" -- may want to discuss and agree upon what is and isn't allowed outside of their relationship. One agreement may be the use of condoms with casual partners to avoid the transmission of STIs and, subsequently, an increased risk of HIV transmission.
Your sexual health from Managing your health, CATIE's guide for people living with HIV
HIV viral load, HIV treatment and sexual HIV transmission -- CATIE Fact sheet
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James Wilton is the coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James is currently completing his master's degree of Public Health in Epidemiology at the University of Toronto and has completed an undergraduate degree in microbiology and immunology at the University of British Columbia.
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