"Blame" is a moral word, and hence contentious. Let's instead use words like "causation", "knowledge," and "foreseeability."

Consider someone who got AIDS via needle-sharing. Clearly, they took actions (sharing a needle) that caused the harm in a "but-for" sense. They knew (or can be deemed to have known ) that sharing needles risks spreading blood-borne pathogens, of which AIDS is one. The harm was clearly foreseeable. So it's quite correct to say that they caused themself to get AIDS. Indeed, if the addict had injected someone else in their sleep, which caused the injectee to get AIDS, no-one would be saying that the addict didn't cause the injectee's illness. Similar analysis applies for unprotected sex.

Now, whether you want to consider that "blameworthy" is complicated. Maybe you don't think that blame is a meaningful concept, or that the "true blame" lies with the person's genetics that predisposed them to addiction, or with their upbringing, or with drug dealers, or society generally, or whatever else. And sure, all of those other factors may well have contributed too. Which one is truly "blameworthy" is not, to me, an interesting debate.

So, if I meet someone with AIDS, I assume they probably did something avoidable and risky that caused themselves to get AIDS. On rare occasions this heuristic may be false, but in general it is a very accurate heuristic. You can call this "victim-blaming" if you like, but I don't see any a priori reason that people can never be the authors of their own misfortune.