People who are living with HIV should take medicine to treat HIV as soon as possible. HIV medicine is called anti-retroviral therapy, or ART. If taken as directed, HIV medicine reduces the amount of HIV in the body (viral load) to a very low level, which keeps the immune system working and prevents illness. This is called viral suppression -- defined as having less than 200 copies of HIV per milliliter of blood. HIV medicine can even make the viral load so low that a test can't detect it. This is called an undetectable viral load. If you are virally suppressed or have an undetectable viral load, your HIV is under control.
Getting and keeping your HIV under control is the best thing people living with HIV can do to stay healthy. Another benefit of reducing the amount of virus in the body is that it helps prevent transmission to others through sex or needle sharing, and from mother to child during pregnancy, birth, and breastfeeding. This is sometimes referred to as "treatment as prevention." There is strong evidence about treatment as prevention for some of the ways HIV can be transmitted, whereas more research is needed for other ways.
People living with HIV who take HIV medicine as prescribed and get and keep an undetectable viral load have effectively no risk of transmitting HIV to their HIV-negative sexual partners.
Transmission From Pregnancy, Labor and Delivery
If a woman living with HIV can take HIV medicine as prescribed throughout pregnancy, labor, and delivery and if HIV medicine is given to her baby for 4-6 weeks after delivery, the risk of transmission from pregnancy, labor, and delivery can be reduced to 1% or less.
Transmission From Sharing Needles or Other Injection Drug Use Equipment
We don't know whether getting and keeping HIV under control prevents HIV transmission through sharing needles or other injection drug equipment. While we do not yet know if or how much being undetectable or virally suppressed prevents some ways that HIV is transmitted, it is reasonable to assume that it provides some risk reduction.
Transmission From Breastfeeding
We don't know if a woman living with HIV who has her HIV under control can transmit HIV to her baby through breastfeeding. While we do not yet know if or how much being undetectable or virally suppressed prevents some ways that HIV is transmitted, it is reasonable to assume that it provides some risk reduction.
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[Note from TheBody.com: This article was originally published by the Centers for Disease Control and Prevention on Dec. 1, 2017. We have cross-posted it with their permission.]