HIV case definitions

Not all AIDS-defining disorders have the same prognosis or outlook. For example, someone with a single lesion of Kaposi's sarcoma has AIDS, but may well have a better outlook than someone with Pneumocystis jirovecii, another common AIDS-defining disorder. Age, race, gender, lifestyle factors, and quality of health care can also mean that people who have the same rigidly defined HIV illnesses may have very different experiences and prospects.

Nevertheless, rigid definitions can be very useful in some circumstances. For example, in clinical and epidemiological studies when large populations of people are being observed, it is essential to have well-defined 'end points' which mark the transition from one state of health to another.

Definitions of HIV and AIDS as they have evolved have come to suggest that HIV infection is an inevitable, one-way process. The implication is that persons with HIV will initially be well, then have abnormal test results a short while before experiencing mild illness, and finally experience a severe terminal illness. This can be the pattern when treatment options are limited and/or HIV infection is diagnosed late.

Persons who are diagnosed at an early stage of infection, or even with an AIDS-defining condition, can become healthy again and remain so for a long while. Furthermore, many people with HIV infection have never experienced any symptomatic diseases, even after many years.