Clinical Progression of HIV

Typical course of HIV infection that shows the relationship between the levels of HIV (viral load) and CD4+ T cell counts over the average course of untreated HIV infection.

Acute Primary Infection

Once HIV enters the body, the virus infects a large number of CD4+ T cells and replicates rapidly. During this acute phase of infection, the blood has a high number of HIV copies (viral load) that spread throughout the body, seeding in various organs, particularly the lymphoid organs such as the thymus, spleen, and lymph nodes. During this phase, the virus may integrate and hide in the cell’s genetic material. Shielded from the immune system, the virus lies dormant for an extended period of time. In the acute phase of infection, up to 70 percent of HIV-infected people suffer flu-like symptoms.

The Immune System Strikes Back

Two to 4 weeks after exposure to the virus, the immune system fights back with killer T cells (CD8+ T cells) and B-cell-produced antibodies. At this point, HIV levels in the blood are dramatically reduced. At the same time, CD4+ T cell counts rebound, and for some people the number rises to its original level.

Clinical Latency

During this phase, a person infected with HIV may remain free of HIV-related symptoms for several years despite the fact that HIV continues to replicate in the lymphoid organs where it initially seeded.

Progression to AIDS

The immune system eventually deteriorates to the point that the human body is unable to fight off other infections. The HIV viral load in the blood dramatically increases while the number of CD4+ T cells drops to dangerously low levels. An HIV-infected person is diagnosed with AIDS when he or she has one or more opportunistic infections, such as pneumonia or tuberculosis, and has fewer than 200 CD4+ T cells per cubic millimeter of blood.