Racial Differences in Susceptibility to Infection byMycobacterium tuberculosis

The prevalence of tuberculosis among blacks is known to be about twice that among whites. When we looked at infection rates among the initially tuberculin-negative residents of 165 racially integrated nursing homes in Arkansas, we were stimulated to investigate whether this difference could be due in part to racial differences in susceptibility to Mycobacterium tuberculosis infection. A new infection was defined by an increase of ≥12 mm of induration after a tuberculin skin test (5 tuberculin units) administered at least 60 days after a negative two-step test.