In high-income countries like the U.S., the standard of care for people infected by HIV is to provide antiretroviral pills when the virus is found, even when there are no symptoms of AIDS. The strategy staves off the disease and has a second – big – benefit. It's been shown to prevent the spread of HIV in sexual encounters. It's called "treatment as prevention" (TasP in medical jargon), or "test and treat."
But in low-income countries, "test and treat" is not the typical approach to prevention. There's been no research to support it.