Let me assume, like most people you also are firmed that HIV is AIDS. I am not good on this medical issues. Sharing what I know.
HIV is the virus that causes AIDS, but that doesnot mean anyone infected with HIV will have AIDS immediately. Sometimes it takes long time, sometime times it doesnot happen, sometimes it affect immediately. You heard that song Pari hu main from Sunita Rao? I read smewhere she was found HIV positive in 1998, its 14 years she is still okay.
In usual cases ELISA blot test is done, it gives an immediate result. Most cases if you have doubt, one test is not enough, you need to go throgh at least a year with 3/4 tests. That can confirm HIV is turning towards AIDS or not. If the body immunity system can prevent, HIV virus would stay in body but wont grow. When it cant prevent, someone fall for it. But a direct blood trasfution often doesnot give scope of immunity. Thats why its better to stay cautious.
All the prostitutes in Thailand, its mandatory to use condom and mandatory to carry the health card which shows they have HIV test taken in last 4 weeks or less.