Transmission of TB

This study into a contact investigation in a UK school gives some interesting data to play with. At the outset of the 765 students and 172 staff tested there were 55 with LTBI and 12 with active TB. So you could say that overall the transmission rate was ~7%.

As no adults were found to be positive it could be assumed that adolescents are more susceptible to TB. The rate of transmission increased with contact, of those tested who were in the same year around 30% were positive.

This appears to indicate that the closer you are to an active TB case the greater the chance that you will get TB.

So general "ball park" rates are not helpful guides to virulence, proximity is the critical factor.