No. HIV is a virus, while AIDS is a stage of advanced infection. Specifically, HIV, or the human immunodeficiency virus, is an infectious virus that gradually breaks down a person’s immune system, leaving the body less able to defend itself against viruses, bacteria, fungi, and parasites. AIDS, or acquired immunodeficiency syndrome, is the stage of the disease when the immune system is weakened by the loss of CD4 cells (also called T-helper or T-4 cells) — white blood cells that help fend off harmful pathogens in the body. AIDS is diagnosed when a person has a CD4 count of less than 200 (meaning less than 200 cells per cubic millimeter of blood) or has at least one of 27 AIDS-defining conditions outlined by the Centers for Disease Control and Prevention (CDC), such as recurrent pneumonia and some lymphomas.

2. Which Activities Are Most Likely to Transmit HIV?

Here is the estimated probability of acquiring HIV from an infected source, per exposure act, according to the CDC:

• Receptive anal sex: 1 in 72
• Shared injection drug use: 1 in 159
• Insertive anal sex: 1 in 909
• Receptive penile-vaginal sex: 1 in 1,250
• Insertive penile-vaginal sex: 1 in 2,500

3. How Long Can I Wait Before Starting Treatment?

Ideally, you shouldn’t wait at all. In the past, doctors would delay treatment until a person’s CD4 count fell below 500 — largely because of concerns about the long-term effects of HIV treatment and the premature development of a drug-resistant virus — but that’s no longer the case.