Some viruses, such as the ones that cause the common cold or the flu, stay in the body only for a few days.
Some viruses, such as HIV, never go away. When a person becomes infected with HIV, that person becomes “HIV positive” and will always be HIV positive. Over time, HIV disease infects and kills white blood cells called CD4 lymphocytes (or “T cells”) and can leave the body unable to fight off certain kinds of infections and cancers.
AIDS stands for Acquired Immuno–Deficiency Syndrome. A healthy person usually has a CD4, (white blood cells) count of between 600 and 1,200. When the CD4 count drops below 200, a person's immune system is severely weakened, and that person is then diagnosed with AIDS, even if he or she has not become sick from other infections.
CellsThink of AIDS as advanced HIV disease. A person with AIDS has an immune system so weakened by HIV that the person usually becomes sick from one of several opportunistic infections or cancers such as PCP (a type of pneumonia) or KS (Kaposi sarcoma), wasting syndrome (involuntary weight loss), memory impairment, or tuberculosis (TB). If someone with HIV is diagnosed with one of these opportunistic infections (even if the CD4 count is above 200), he or she is said to have AIDS. AIDS usually takes time to develop from the time a person acquires HIV – usually between 2 to 10–15 years.
Once a person has been diagnosed with AIDS, she or he is always considered to have AIDS, even if that person's CD4 count goes up again and/or they recover from the disease that defined their AIDS diagnosis.
After the diagnosis of AIDS is made, the current average survival time with antiretroviral therapy is estimated to be now more than 5 years, but because new treatments continue to be developed and because HIV continues to evolve resistance to treatments, estimates of survival time are likely to continue to change. Antiretroviral medication can prolong the time between HIV infection and the onset of AIDS. Without antiretroviral therapy, death normally occurs within a year. Most patients die from opportunistic infections or malignancies associated with the progressive failure of the immune system.