The prevalence of intradermal sensitivity to various mycobacterial antigens in a group of healthy children in southeastern United States

Two hundred seventy-four healthy white school-age children residing in a children's home in northwestern North Carolina were tested intradermally with 5 tuberculin units of PPD-Watson (Group II), PPD-Battey (Group III), PPD-S (Mycobacterium tuberculosis), and PPD-Phlei (Group IV). Ninety per cent of the children had at least one positive reaction (2 mm or more of mean induration) at one or more of five readings (24 hr, 48 hr, 72 hr, 96 hr, and 168 hr). The most frequent reactions were to PPD-Watson. In 22 children, positive responses to PPD-S were probably cross-reactions as a result of infection with one or more atypical mycobacteria.