HIV is the virus that causes the disease AIDS. Although HIV causes AIDS, a person can be infected with HIV for many years before AIDS develops.
When HIV enters your body, it infects specific cells in your immune system. These cells are called CD4 cells or helper T cells. They are important parts of your immune system and help your body fight infection and disease. When your CD4 cells are not working well, you are more likely to get sick.
Usually, CD4 cell counts in someone with a healthy immune system range from 500 to 1,800 per cubic millimeter of blood. AIDS is diagnosed when your CD4 cell count goes below 200. Even if your CD4 cell count is over 200, AIDS can be diagnosed if you have HIV and certain diseases such as tuberculosis or Pneumocystis carinii [NEW-mo-SIS-tis CA-RIN-nee-eye] pneumonia (PCP).
There are general stages of HIV infection that you may go through before AIDS develops.
Infection. The earliest stage is right after you are infected. HIV can infect cells and copy itself before your immune system has started to respond. You may have felt flu-like symptoms during this time.
Response. The next stage is when your body responds to the virus. Even if you don’t feel any different, your body is trying to fight the virus by making antibodies against it. This is called seroconversion, when you go from being HIV negative to HIV positive.
No symptoms. You may enter a stage in which you have no symptoms. This is called asymptomatic infection. You still have HIV and it may be causing damage that you can’t feel.
Symptoms. Symptomatic HIV infection is when you develop symptoms, such as certain infections, including PCP.
AIDS. AIDS is diagnosed when you have a variety of symptoms, infections, and specific test results. There is no single test to diagnose AIDS.