The association between the incidence of TB in the
country of birth and the incidence of TB among
migrants found in this study is likely to be conservative.
Most cases of TB among migrants occur within
several years of migration,9 and the current year’s risk
of TB in the country of birth may not be a good indicator
of the historical exposure of migrant populations
in Australia and Canada. The decreased ability
of the rate of TB in the country of birth to predict the
rate of TB among migrants in Canada compared with
Australia is primarily associated with the lack of data
available for migrant groups in Canada with a low
incidence of TB. The smaller size of some migrant
populations in Canada is also likely to be associated
with greater variability in the estimates of TB rates in
these populations. As the small size of the data set
available for this analysis may have limited our findings,
further studies involving other migration receiving
countries are recommended.