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 scrofulacaeum 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 and average of 0.45% persons reacted with indurations > or = 10 mm to PPD. An average of 7.76% if army recruits reacted with indurations > or = 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 mm and 15 mm were classified as false-positive. A total of 16% with indurations > or = 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.