My only problem with that is it just seems kinda "comic book-ish" to me, which for the level and degree of reality put into the story would be just too hard to swallow. Like the geneticist, or terrorist group thing, or so many other ideas (excluding the growth and mutation stuff), I just can't buy into most if not any of them. The simplest and most believable idea to me is that this shit just happened, and now they gotta deal with it, maybe never having found out exactly what caused it except for best guesses, and by the end everybody's just gotta start over and get on with their lives having collectively experienced a near extinction event. That doesn't mean some crazy shit isn't going to happen from now till then.