Interventions for Tuberculosis Control and Elimination
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In the trial in the United Kingdom (using M. microti rather than BCG), persons with a negative tuberculin skin test to the usual test dose were also tested with 100 tuberculin units. Those reacting only to this high dose are likely to have been infected with an environmental mycobacterium. As shown in the graph the risk of tuberculosis in this group during follow-up was smaller than that among those not reacting to any dose of tuberculin. This strongly suggests that sensitization with environmental mycobacteria provided some protection against tuberculosis resulting from subsequent infection with M. tuberculosis.
