My guess is that's not a concern. Like most teen idols, sooner than later he's going to want his image to grow up, and I think his increasingly public relationship with Selena is part of that. I don't think he's going for the full bad boy, but I do think he wants his fans to let him grow up at some point. I think the first is far more likely. The idea of "picking girls out to meet Justin" is actually part of the way they do the shows - there's one song where they pick a girl from the audience to sit on stage while Justin sings to her, and they also regularly move people up from the bad seats, or hand out good tickets to people before the shows start. In other words, it's believable that this woman could have been invited backstage, but frankly not to pop Justin's cherry. I mean seriously - if such a service was actually required (!), there would be literally millions of potential candidates, and the venue would likely not be an arena bathroom. Similarly, the woman's story that he told her it was his first time is either just wishful thinking on her part, or a line from a guy who's used it more than once. From what I can tell, Justin has a really solid core group of people around him who have been with him from the start. Surely they would have schooled him on the dangers of golddigging groupies, safe sex etc - and he's not a choirboy on his own either, even if looks like one. He'd know all this stuff himself I think. It would be easy enough to do a DNA test to disprove this, but at the same time, I wonder if they will refuse or at least fight it - if he wants to protect his privacy, I would think that would include not making his DNA available to any girl that makes an accusation.