Overview

The World Health Organization (WHO) classifies HIV infection into 4 stages:^{footnote 1}

WHO stages of HIV infection

• Stage 1 (HIV infection): The CD4+ cell count is at least 500 cells per microlitre.
• Stage 2 (HIV infection): The CD4+ cell count is 350 to 499.
• Stage 3 (advanced HIV disease, or AHD): The CD4+ cell count is 200 to 349.
• Stage 4 (AIDS): The CD4+ cell count is less than 200 or the percent of CD4+ cells is less than 15% of all lymphocytes.

The U.S. Centers for Disease Control and Prevention (CDC) classifies untreated HIV infection into 3 stages:^{footnote 1}

CDC stages of HIV infection

• Acute retroviral syndrome: This is an illness with symptoms like mononucleosis. It often develops within a few days of infection with HIV, but it also may occur several weeks after the person is infected. The symptoms can range from mild to severe and usually disappear on their own after 2 to 3 weeks. But many people do not have symptoms or they have such mild symptoms that they don't notice them.
• Stage 1 (HIV infection): There are no AIDS-related conditions AND the CD4+ cell count is at least 500 cells per microlitre or the percent of CD4+ cells is at least 29% of all lymphocytes.
• Stage 2 (HIV infection): There are no AIDS-related conditions AND the CD4+ cell count is 200 to 499 or the percent of CD4+ cells is 14% to 28% of all lymphocytes.
• Stage 3 (AIDS): The CD4+ cell count is lower than 200, the percent of CD4+ cells is less than 14% of all lymphocytes, or an AIDS-related condition is present.

In general, the higher the CD4+ count, the less likely it is that opportunistic diseases will occur. Most people who have untreated HIV experience a gradual drop in the number of CD4+ cells. Each person responds uniquely to this decline.