Ah, therein lies the fun. You can't refer them as a pretext to not treat them because they are HIV positive, but you can refer for a legimate reason, ie. you are not qualified or feel someone is better qualified to treat them.
Also on a similar note, as an attorney, I am obliged to say that anything I write here is not my legal opinion and does not constitute legal advice in any way, shape, or form. I know its ridiculous that I need to do that, but you'd be amazed (not really) at what people will sue over.
So basically...lie.
You can't say it is because the patient has aids, so you shove them off on another person because you don't feel qualified to handle a person with HIV/AIDS. 😛