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What does an undetectable HIV viral load mean for sexual transmission?

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AIDS Scanning electron micrograph of HIV-1 virions (green) budding from a cultured lymphocyte. Multiple round bumps on the cell surface represent sites of virion assembly and budding.

When an individual living with HIV adheres to antiretroviral therapy over the long term, their HIV viral load can reach levels that are considered undetectable. In the context of sexual health, this means that the virus cannot be transmitted to sexual partners. This medical phenomenon is widely referred to as "undetectable = untransmittable," or U = U.1

Achieving an undetectable viral load is a critical goal of treatment, as it effectively eliminates the risk of sexual transmission of the virus. It is important to note that while the virus becomes undetectable in the blood, it may still persist in latent reservoirs within the body, such as in certain immune system cells. Therefore, consistent adherence to prescribed medication is essential to maintain an undetectable status and prevent the virus from rebounding.12