Investigation into typical and atypical tuberculin sensitivity in the Royal Netherlands Army, resulting in a more rational indication for isoniazid prophylaxis

Setting: The Department of Military Health Services (DMGZ) vaccination clinic, Utrecht, The Netherlands. Objectives: To improve upon PPD skin testing procedure by introducing a double Mantoux test. Design: During the first part of the study, from 1986-1988, army recruits were double-tested simultaneously with PPD and Mycobacterium scrofulaceum sensitin. During the second part of the study, from 1989 to 1993, recruits reacting to PPD, with an induration in the range of 10-15 mm, underwent a second skin test with M. scrofulaceum sensitin. The total study population consisted of 237 692 non-BCG-vaccinated recruits. Results: From 1986-1993 an average of 0.45% persons reacted with indurations greater than or equal to 10 mm to PPD. An average of 7.76% army recruits reacted with indurations greater than or equal to 10 mm to M. scrofulaceum sensitin during the first part of the study. Using a modified ITSC (International Tuberculosis Surveillance Centre) model, 48% of the persons reacting to PPD with indurations in the range 10 mn and 15 mm were classified as false-positive. A total of 16% with indurations greater than or equal to 10 mm to PPD were classified as false positive. False-positive persons were then excluded from INH chemoprophlaxis, Conclusions: In areas with a high prevalence of non-tuberculous mycobacteria infection the use of double skin testing might be useful in differentiating between indurations due to tubercle bacilli and those due to infection with non-tuberculous mycobacteria.