You can have TB without having virulent TB. In fact, in western countries, if we discover infection we treat. If you have TB, your risk of becoming symptomati

You can have TB without having virulent TB. In fact, in western countries, if we discover infection we treat. If you have TB, your risk of becoming symptomatic is only about 1% per year, however you are potentially contagious the entire time. So in the health community we conduct TB screening, and most migrants are required to either show evidence of BCG status, or a series of chest x-rays often combined with the results of a Mantoux test. A friend of mine, an emergency trainee, recently changed hospitals and had to have another Mantoux test. He lived in shanghai as a kid and would have been exposed in some manner, even though his body either cleared it or it is long dormant (his CXRs are clear). NSW health policy is that he needs 6 months of a course of antibiotics to ensure it is not latent in him. The same approach is taken to would be migrants. So you see, with tb the issue is not so much virulence, but our ability to control its spread in the community and prevent a potential pandemic of XDR TB, which all of a sudden would have TB as big of a public health threat as it was 50 years ago