What condition is indicated by a CD4+ T lymphocyte count below 200 cells/µL?

A CD4+ T lymphocyte count below 200 cells/µL is a critical indicator of immune system compromise and is specifically associated with the progression of HIV infection to AIDS (Acquired Immunodeficiency Syndrome). The CD4+ T lymphocytes play a vital role in the immune system, helping coordinate the body's response to infections.

When the CD4+ count falls below this threshold, it signifies a significantly weakened immune system, making the individual highly susceptible to opportunistic infections and certain cancers that are hallmarks of AIDS. This numeric cutoff is widely used in medical guidelines to make a definitive diagnosis of AIDS, as it reflects the severity of immunosuppression associated with chronic HIV infection.

Other conditions listed, such as chronic fatigue syndrome, advanced liver disease, and acute bacterial infection, do not have a direct correlation with CD4+ T lymphocyte counts below this threshold. Thus, the significance of the number in relation to AIDS diagnosis establishes it as the correct choice in this question.