Prevalence of mycobacterial sensitivity in Montreal children.

The prevalence of sensitivity to atypical mycobacteria was found to be low in 2152 Montreal first-grade children tested with tuberculin and one of four atypical antigens randomly allocated. Forty-nine had positive reactions to an atypical antigen. PPD-G produced more reactions than PPD-A, -B or -K. In Greater Montreal there was a higher prevalence of sensitivity to atypical mycobacteria than in the two suburban areas studied. The range of this prevalence, standardized for the type of antigen, was from 0.86 to 2.92% according to region. The highest prevalence of sensitivity to any single atypical antigen, 5.3%, was found for PPD-G in Greater Montreal.Tuberculous infection was found in 1.35% of the children. Small tuberculin reactions (5 to 9 mm to stabilized PPD 5 TU) require clarification by differential tuberculin testing. More of them are caused by M. tuberculosis than by atypical mycobacteria in this particular age group and region.Routine BCG immunization is not indicated for the particular population studied; when given to individuals at risk, its effectiveness should not be impaired by atypical sensitivity at the low level found locally. Future BCG plans require more epidemiologic data.