Transmission characteristics of tuberculosis in the foreign-born and the Canadian-born populations of Alberta, Canada.

SETTING

All notified cases of tuberculosis in the province of Alberta, Canada, 1994-1998.

OBJECTIVE

To compare the transmission characteristics of tuberculosis among foreign-born and Canadian-born cases.

DESIGN

Retrospective analysis using DNA fingerprinting (IS6110 restriction fragment length polymorphism and spoligotyping) and patient information from the Alberta Tuberculosis Registry. Transmission indexes were determined by calculating the average number of culture-positive pulmonary cases generated by a single source case.

RESULTS

Of the 750 cases of active tuberculosis, 437 (58.3%) were in the foreign-born. DNA fingerprinting of Mycobacterium tuberculosis isolates from all 573 culture-positive cases over the 5 years from 1994 to 1998 showed that there was significantly less clustering among foreign-born isolates (9.8%) compared to Canadian-born non-Aboriginal (28.8%) and Aboriginal (44.7%) isolates. The transmission index was significantly higher for males, lower for those > or =65 years of age, and higher for Aboriginals.

CONCLUSION

Although cases of tuberculosis in the foreign-born constitute the majority in Alberta, there is little transmission to other foreign-born or to Canadian-born individuals. Transmission of tuberculosis among the Aboriginal population remains a significant problem in Alberta.