Density of tuberculin skin reaction and its association with tuberculosis infection as defined by dual tuberculin testing

OBJECTIVE: To determine whether the density of tuberculin skin reactions is associated with tuberculosis infection. METHODS: In a national tuberculin survey in Tanzania, 1983-1987, all eligible children in a random sub-sample of schools underwent dual tuberculin skin testing with PPD-RT23 and PPD-scrofulaceum. The density of reactions to RT23 was classified as proposed by Palmer. A larger reaction to PPD-scrofulaceum than to PPD-RT23 is suggestive of infection with environmental mycobacteria. Tuberculosis infection was defined based on dual skin test results applying a range of possible definitions. RESULTS: A total of 10 782 children aged 5-14 years and without BCG scar were included in the analysis. Large skin reactions to RT23 were generally firmer than small ones. After taking the size of the skin reaction to RT23 into account, its density was not associated with the size of the skin reaction against PPD-scrofulaceum. In particular, the density of reactions in the range 6-11 mm was not associated with tuberculosis infection according to any of the definitions used. CONCLUSION: This study suggests that the density of reaction was not associated with tuberculosis infection in Tanzanian school children after taking the size of the induration into account.