The human immunodeficiency virus (HIV)

The human immunodeficiency virus (HIV) is the virus that causes AIDS (acquired immunodeficiency syndrome). The virus gets its name because it infects and damages part of the immune system — the body's natural defense system.

Often the only way to know if someone is infected with HIV is through testing. That's because people who are HIV positive may not know that they have the virus. Most of the signs that someone has HIV don't show up until that person has developed full-blown AIDS. By that point, the person is sicker and the disease can be harder to treat.

Here are the facts on what's involved in getting tested — and who should get tested for HIV and why.