This sounds like typically uninformed inflammatory talk radio shenanigans - I'm not sure I've heard any reputable source discuss this as a 'trend' outside of anything but a VERY small niche portion of the gay community, and even there it is more of a fetish than a reality (
here is a pretty poor Wikipedia entry about this particular phenomenon, albeit mostly directed on the 'receiving' side).
While some may be actively trying to infect others for some sort of personal pleasure, most are probably not actively seeking to infect - rather, limited cases (such as
this one in Iowa a while back) indicate that the scenario is likely something done out of shame, and not necessarily malice or whatever. I've never really seen much in the way of proof indicating a sort of 'sociopathic' bent to spreading the disease, and it seems somewhat far-fetched to discuss this as a 'trend' even as HIV/AIDS numbers are dropping in the USA (and worldwide).
However, if you live in a state that has laws about
criminal transmission of HIV you should most certainly call the police - there is certainly a moral obligation to inform partners of your status, and there may be a legal obligation as well.
In any case, though, even these extremely slight corner-case percentages underscore why it's important to take control of your own personal health whenever you have sex.