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The need for definitions
In reality, not all AIDS-defining disorders have the same prognosis, or outlook. For example, a gay man with a single lesion of Kaposi's sarcoma has AIDS, but has a better outlook than a gay man with PCP, another common AIDS-defining disorder. Age, race, gender and lifestyle factors can also mean that people who have the same defined HIV illnesses may have very different 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. This is the only way that scientific principles can be observed and the studies can reach firm, reliable conclusions. It is also appropriate that these definitions change from time to time, as the epidemic evolves and we find out more.
However, definitions of HIV and AIDS as they have evolved have come to suggest that HIV infection is an inevitable, one-way process. In other words, they imply that everyone with HIV will initially be well, then they will get abnormal tests a little while before they get mild illness, and finally there will be a severe terminal illness.
This has been the pattern for many people, but others have had very different experiences. For example, people can get infections that would be diagnostic of AIDS and then become healthy again for a long while. This may be because their immune systems were damaged by a combination of HIV and another, temporary co–factor which went away (for example, stress or another infection). Furthermore, many people with HIV infection have never experienced any symptomatic disease after many years.