That again is a good question. It's difficult. If you don't look for it, you don't know if a person has it. I would suspect the vast majority of people in Canada who are infected will come back from having travelled with no symptoms or with mild symptoms and they won't get tested. We won't know about them.
The only time we know if someone has Zika is when blood goes to Matt's lab and we find the virus present in the blood or there's a suggestion from their antibodies that someone has it. That's all. So far, as I mentioned, 20 people in Canada have tested positive. I'm confident and I'm sure the numbers are much higher than that, but the only way we can detect it is if we test people.