Objective: To determine the degree of and variation in sensitivity to PPD RT 23 tuberculin and M. scrofulaceum sensitin RS 95 at school age in children BCG vaccinated at birth.
Design: Double-testing by applying standard WHO Mantoux tests and inspecting BCG scars.
Setting and participants: Urban and rural schools in Southwest Finland, 1091 children aged 11-13 years.
Main outcome measures: Size of tuberculin and sensitin indurations and BCG scar (mm).
Results: The mean size of tuberculin indurations was 7.2 mm, sensitin indurations 8.1 mm and BCG scars 7.9 mm. The reaction to sensitin was significantly larger than to tuberculin (95% confidence interval 0.58-1.10 mm) and the zero reactions to sensitin were fewer. Correlation between tuberculin and sensitin indurations was significant (r = 0.75, 95% confidence interval 0.72-0.77). There were induration greater than or equal to 15 mm to tuberculin in 16% and to sensitin in 14%. Sensitin indurations exceeded those of tuberculin by 4 mm or more in 14% of the children with at least 5 mm tuberculin indurations.
Conclusions: High tuberculin sensitivity in healthy schoolchildren may be partially maintained by contact with environmental mycobacteria. Our data do not prove but very probably indicate that children have protective immunity. In view of the current incidence of tuberculosis in Finland and the likelihood that lymph node infections and sensitivity to environmental mycobacteria will increase, continued BCG vaccination at birth is recommended.