Risk of active tuberculosis in immigrants: effects of age, region of origin and time since arrival in a low-exposure setting.

OBJECTIVE: To estimate the risk of active tuberculosis (TB) in immigrants to VICtoria, Australia, as a function of time since arrival and stratified by age group and region of origin. DESIGN, SETTING AND SUBJECT: Longitudinal study of the incidence of active TB in VICtorian immigrants, excluding New Zealanders, who arrived in Australia between 1975 and 2007. VICtorian immigration data were used to describe annual arrival cohorts by age and region of origin, and TB case notification data for 1995 to 2010 were matched to the cohorts. Survival analysis was performed to determine incidence rates of active TB. MAIN OUTCOME MEASURES: Incidence of active TB, stratified by age, region of origin and time since arrival in Australia.
RESULTS: Incidence of active TB following immigration to Australia was highly dependent on region of origin, with the highest risks being in immigrants from South Asia and sub-Saharan Africa. For immigrants from high-risk regions (Asia, Africa and the Pacific), the incidence of active TB infection was 100-150 per 100 000 person-years in the first 6 years following immigration. Overall, we estimate that 50% of TB occurred within 7 years of arrival. A bimodal age distribution was evident, with peaks of incidence in 20-24-year-olds and 70-74-year-olds.
CONCLUSIONS: Our data show that substantial risk of TB in VICtorian immigrants persists well beyond the first 2-3 years following arrival, and that risk is highly dependent on region of origin. The regional dependence suggests that public health strategies would benefit from more refined regional stratification of risk, which could be used to determine risk thresholds for the use of TB prevention strategies and predict rates of TB in Australia following particular patterns of immigration.