When someone is living with HIV it means that HIV is present in their body. As HIV is present in semen, vaginal fluid and the anal secretions of a person who is HIV positive there may be a risk from HIV transmission if you are engaging in sexual activity with them.
In order for sexual transmission of HIV to occur there must be:
At least one person living with HIV (HIV positive)
At least one person who is not living with HIV (HIV negative)
And at least one type of unprotected sexual activity between these people
To avoid sexual transmission of HIV the most effective way of all is to:
Know your own sexual health status by having a full sexual health screening.
Know the sexual health status of your sexual partner(s)
Sometimes you may decide to share sexual activity with people who cannot tell you their sexual health status. You may never have had this conversation with your current partner for example. This means that they don't know if they are living with HIV, so you don't know if you can contract it from them.
Unprotected sexual activities that carry a risk of HIV transmission include: