It is well established that old people living in institutions are more susceptible to tuberculous reactivation and exogenic infection than the general population. Therefore, annual screening with a tuberculin (T) skin test is suggested. Unfortunately, the specificity and sensitivity of this test is limited because of cross-reactivity with non-tuberculous mycobacteria (NTM) and anergy. We therefore investigated the possibility that a simultaneous test with NTM antigen might be helpful in the interpretation of the T test in the elderly. We tested 220 inhabitants of a geriatric institution in Israel simultaneously with T and Mycobacterium scrofulaceum sensitin (S). Ninety-six subjects reacted to the T test, and 64 of them reacted to S as well. In this last group, 38 reacted more to T, 22 more to S, and 4 reacted equally to both antigens. Of the 124 subjects who did not react to T, 24 did react to S and 123 were retested with T. Twenty-two of the latter group had a positive booster effect, but 9 of the positive booster responders initially reacted to S. The difference between the proportions of the positive booster effect in the responders and the non-responders to S was significant. We conclude that in an area where infection with NTM is present a simultaneous S test may clarify the meanings of initial and booster-positive responses to T in the elderly, as well as exclude anergy when the T test is negative.
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