Acquired immunodeficiency syndrome

Acquired immunodeficiency syndrome, commonly AIDS, is the most severe stage of infection with a human immunodeficiency virus. Damage to immune defenses allows serious opportunistic infections and other characteristic illnesses. HIV-1 is a virus; acquired immunodeficiency syndrome is a clinical syndrome associated with advanced disease, not another name for the viral particle or for every positive infection test. Effective antiretroviral treatment can prevent progression to this stage.^[ref]

An early observation was a cluster of unusual infections rather than a direct measurement of a newly identified virus. The CDC's5June1981 report described five young men treated at three Los Angeles hospitals for biopsy-confirmed Pneumocystis pneumonia. The report also described other infections and profoundly reduced in-vitro proliferative responses in the three patients whose lymphocyte function was tested.^[ref]

The denominator matters: three abnormal tests out of three tested patients is not evidence that all five were tested, nor does it estimate the frequency of immune dysfunction in a general population. The pattern motivated investigation of a shared immunodeficiency, while the case series alone did not establish its cause or route of transmission.

The scientific distinction remains useful. An organism that is usually controlled can become pathogenic when host defenses fail; investigating the infection and investigating the underlying immune defect answer different questions. Conversely, a single nonspecific symptom cannot establish acquired immunodeficiency syndrome, and a human immunodeficiency virus infection need not have progressed to that syndrome.