Antituberculosis drug resistance in immigrants to Alberta, Canada, with tuberculosis, 1982-1994

Provincial Tuberculosis Service, Alberta, Canada.

To estimate resistance rates of Mycobacterium tuberculosis to antituberculosis drugs in relation to previous treatment, country of origin, age and duration of residence in Canada.

Retrospective chart review of all culture-positive tuberculosis diagnosed between 1982 and 1994 in immigrants to Alberta.

A total of 753 immigrants with culture-positive tuberculosis were studied; 131 patients (17.4%, 95% Confidence Interval [CI] 14.7, 20.1) had strains resistant to one or more of the first-line medications (isoniazid [INH], rifampin [RIF], ethambutol [EMB], pyrazinamide [PZA], and streptomycin [SM]). Initial and secondary resistance rates were 16.4% and 30.3%, respectively (P = 0.003, Odds ratio [OR] 2.2, 95% CI 1.3, 3.8). Resistance occurred in 22.2% of patients 40 years of age and under, and in 13.8% of those over 40 years of age (P = 0.005, OR 1.8, 95% CI 1.2, 2.6). Resistant M. tuberculosis was isolated from 20.4% of those who had lived in Canada for less than 15 years, and in 9.0% of those who had immigrated to Canada more than 15 years before diagnosis (P < 0.001; OR 2.4, 95% CI 1.3, 4.2). Resistance rates to individual medications in all immigrants were as follows: INH 9.9% (95% CI 7.8, 12.0), RIF 0.8% (95% CI 0.2, 1.4), EMB 1.9% (95% CI 1.0, 2.8), PZA 1.9% (95% CI 0.3, 3.5), and SM 12.9% (95% CI 10.4, 15.4). Immigrants from Vietnam, China, and the Philippines had tuberculosis strains that were resistant to one or more of the first line medications in 30.2%, 21.8%, and 15.5% of cases, respectively (P = 0.04).

In industrialized countries such as Canada where most cases of tuberculosis are diagnosed among the foreign-born, drug resistance surveys continue to be an important part of an effective tuberculosis control program.