risk per act of getting hiv infection?

Hello and welcome to e health forum.

Yes, that is right.

HIV is a very delicate virus, and chances of transmission of having HIV, from a single unprotected sexual encounter (via vaginal ‎sex) is 0.04% (female to male) per act, which ‎is very low to cause a confirmed infection, just by a single act‎.

The fact is having sex once with somebody whom you know to be HIV positive does not guarantee you will get the virus. Continuous and regular sex with a HIV positive person for some time, does increase the chance of acquiring HIV.

There are a lot of instances where HIV negative partners of HIV positive patients, have not acquired HIV via ‎intercourse. But it does not mean that people should not follow safe sex, and take a risk. The chances that reduce the risk include - low viral loads in the patient, proper anti retroviral therapy for HIV, and following safe sex.