The chances of getting HIV from a single sexual encounter are low, but they are not zero. Estimates suggest that about 4 to 8 infections occur per 10,000 acts of vaginal intercourse with an HIV-positive partner, and about 11 to 138 infections per 10,000 acts of anal intercourse.
However, the chances of getting HIV also depend on whether the HIV-positive person is receiving HIV treatment. When a person with HIV takes antiretroviral therapy (ART) correctly and has an undetectable viral load on blood tests, the virus is not transmitted through sexual contact.