Tuberculin Sensitivity of Young Adults in the United States

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Abstract
Geographic variations of prevalence of tuberculin sensitivity were mapped from tuberculin tests of over 120,000 Navy recruits and college students from all parts of the country with a 5 TU (0.0001 mg) intradermal test with the international standard PPD. Through-out large sections of the country the percentage of positive reactors was less than 10%, in many areas less than 6%, corresponding to annual infection rates of from about 5 to 2/1000/ year. As frequencies of positive reactors in young adults represent the results of tuberculous infections taking place over the past 2 decades, it is likely that the infection rate is probably now well below 1/1000/year in much of the country. The relative proportion of small and large tuberculin reactions, among those usually regarded as positive, also shows consider-able geographic variation. Most small reactions (5 to about 10 or 12 mm in diameter) are ascribed not to tuberculous infection but to some other sensitizing agent they are nonspecific reactions; whereas most of the large reactions to the 5 TU test represent specific tuberculous infection. Careful measure- ment of tuberculin reactions is therefore essential for efficient identification of persons most at risk of developing clinical tuberculous disease. A high positive correlation was found between frequency of reactors among Navy recruits and tuberculous death rates in the white populations of their home states.