The term "Patient Zero" was actually a misnomer.
Yes - Gary Shilts picked it up and it sort of attained an identification with Gaeten Dugas - that term is, in fact, standard epidemiological terminology for the theoretical first locus of an epidemic, as far back as inferential methods such as contact tracing can be reliably employed. It was never intended to imply that Dugas was the sole carrier - he had to get it from somewhere, after all (and no, it wasn't from buggering monkeys), but that's how it was reported.
Thank you for the link.