after having TB vaccine, OT test must be positive, sometimes very strongly positive. if in China, it's ok since doctors know this is caused by immunization. But, in Canada or US, doctors usually think this is TB infection. the reason they have such dignosis is they don't have much experience for TB because this is a non-TB country. If in nursery school, they know your baby maybe has TB, thet won't let him/her stay there. This case was happened in one of my friend in US. I think it's same thing in Canada. Hope helpful.