Incidence of Pulmonary Disease Caused by Mycobacteria other than Tuberculosis in British Columbia

CONTEXT: The incidence of pulmonary disease due to mycobacteria other than tuberculosis (TB) in Canada has not been documented.

OBJECTIVE: To determine the incidence of pulmonary disease due to mycobacteria in the nonimmunocompromised population of British Columbia.

DESIGN: A retrospective cohort study of 110 cases of mycobacteria infection other than TB identified from 1991 to 1995.

SETTING: British Columbia Centre for Disease Control, Division of TB Control.

RESULTS: The overall incidence rate of infection with mycobacteria other than TB was 0.63×10^-5/year. This incidence rate was significantly higher among women (relative risk [RR]=2, P=0.0006) and in those aged 55 years or older (RR=8, P<0.00001). In contrast with TB, patients were more frequently born in Canada (P<0.00001) or in industrialized countries other than Canada (P<0.00001), and were less likely to be Aboriginal (P=0.0007) or foreign born from Asia (P<0.0001). The most common organism isolated in British Columbia was Mycobacterium avium-intracellulare (82.7%). Overall, 78 (71%) cases had underlying lung disease. Drug intolerance was very common (42%). After treatment, 55% and 41% of the patients were rendered smear negative or culture negative, respectively. Radiological improvement was noted in 55% of patients, and 60% of patients responded symptomatically to treatment.

CONCLUSIONS: The overall incidence of pulmonary disease is low. It is a disease predominantly of women 55 years and older, and targets completely different ethnic groups than TB, suggesting a protective effect of infection with Mycobacterium tuberculosis. M avium-intracellulare was the most common pathogen isolated. Further investigation is required into the natural history of so-called ′colonizers′. Considerable morbidity may be prevented with earlier intervention.