The level of CD4+ T-lymphocytes can drop below 200 μL in the late stage of AIDS, when patients are prone to multiple life-threatening opportunistic infections. After HIV enters the body, it usually reaches the local lymph nodes after 24-48h, and the viral component can be detected in the blood for about 5 days, followed by acute viremia. During the acute phase, there is a transient decrease in CD4+ T lymphocytes. Most patients can recover to normal or close to normal levels on their own without special treatment. However, because the body’s immune system cannot completely clear the virus and form chronic infections, CD4+ T lymph levels will gradually and continuously and slowly decrease. When CD4+ T lymph levels rapidly decrease again to below 350 μL, patients will have a variety of opportunistic infections, and CD4+ T lymph levels can drop to below 200 μL in advanced patients.