The molecular epidemiology of tuberculosis in western Canada.

Objective: To define the molecular epidemiology of TB in western Canada, and in particular the risk factors for clustering.

Measurements: We prospectively identified all positive cultures from newly diagnosed cases of TB diagnosed between February 1995 and January 1997 and carried out restriction fragment length polymorphism (RFLP) testing on all isolates.

Results: Of 956 cases identified, 944 fulfilled the entry criteria. The mean age was 49.65 years (+/- 22.33), and 508 (53.6%) were males. Three hundred and three (32.1%) subjects were clustered; this varied from 20.2% of the foreign born, 48.4% of Canadian non-Aboriginal and 61.1% of all Aboriginal persons. Younger persons (P = 0.0001), males (P = 0.015), those with pulmonary disease (P < 0.001), living in a shelter in the past year (P < 0.001), drug-susceptible disease (P < 0.036), predisposing factors (P < 0.001), prior contact (P < 0.001), and prior skin test (P < 0.002) were more likely to cluster. Among specific risk factors, HIV infection, injection drug use, alcohol excess, and weight loss were all significant.

Conclusions: In this description of the molecular epidemiology of TB in Western Canada, previous results have been confirmed and extended. These results highlight the importance of identifying specific high risk groups, especially in the context of renewed efforts to target persons for treatment of latent TB infection.