"It's a... if he hadn't taken his potions, you could have caught it from him any number of ways," Hermione said.  She seemed to be trying to keep her words as clinical as she could and had leeched all pity from her voice.  "I'd suggest owling him to ask, but even if he says he did take them... there's a test you can have done at St. Mungo's that will tell you if it's... I had to ask for it.  It's not the sort of thing they think of."