Many of those illnesses originally came out of China. Well, Central Asia.
To me and I suspect a number of others, a pandemic is any illness which is deadly and is spreading widely, and often through unidentified means.
Fair enough.
. For a number of years the specific cause of AIDS was unknown, or it was not possible to determine if one was infected/contagious.
Um-mm... yeah... going to have to disagree with you there. AIDS was known to be an STD. There was noting mysterious about it. It was even known as GRID, gay-related immunodeficiency.
AIDS was identified quite early as an STD. However, it took a while longer for people to realize that cases experienced by hemophiliacs, or surgery recipients were HIV and they certainly were NOT STD. I remember the argument over whether gay men should be allowed to provide blood. Also by that time it was spread among addicts and others who sold their blood to buy a fix. I knew a young man who was operating a gay escort service. In 1985, the Washington Post ran a 3 day series on HIV/AIDS. The next time I saw that guy, he said 1/2 his clientele had disappeared. He said these were suburban husbands who were sneaking out on their wives. I imagine there were a few wives who became sick without thinking they had been hit with an STD and some puzzled doctors.