Daniel Hoops is right in saying that individuals with an immune system that is sufficiently compromised can very well develop AIDS-related illnesses and have sufficiently low CD4+ levels, a state that could be characterized as AIDS. In fact, with the reporting systems in place in the United States, there have been several, though rare, HIV-negative AIDS cases reported to the Centers for Disease Control and Prevention (CDC). However, when the CDC (and others) looked into these AIDS-like cases that have no detectable HIV, they found that they were nothing like the usual AIDS cases caused by HIV. They don’t share the same risk factors usually associated with those who get infected with HIV: injection drug use, prostitution, being a man who has sex with men, et cetera. In fact, these cases were due to other underlying diseases. For example, some cases were reported as AIDS because they were cancer survivors who were on immunosuppressants for their transplants and were undergoing chemotherapy. These individuals would indeed exhibit AIDS-like clinical characteristics, but they would be treated for their underlying diseases that caused AIDS-like illnesses and low immune cell counts, and not for HIV – this condition is called idiopathic CD4 lymphocytopenia (ICL) and is not AIDS. Nobody will deny that there are other conditions that cause immune deficiency and that lead to opportunistic infections much like those suffered by AIDS-patients – but AIDS is caused by HIV, period.
MSc II Epidemiology