IMPLICATIONS OF SIMULTANEOUS TESTS FOR TUBERCULIN AND NONTUBERCULOUS MYCOBACTERIA ANTIGEN IN THE ELDERLY

It is well established that old people living in institutions are more susceptible to tuberculous reactivation and exogenic infection than t he general population. Therefore, annual screening with a tuberculin ( T) skin test is suggested. Unfortunately, the specificity and sensitiv ity of this test is limited because of cross-reactivity with nontuberc ulous mycobacteria (NTM) and anergy. We therefore investigated the pos sibility that a simultaneous test with NTM antigen might be helpful in the interpretation of the T test in the elderly. We tested 220 inhabi tants of a geriatric institution in Israel simultaneously with T and M ycobacterium 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 anti gens. Of the 124 subjects who did not react to T, 24 did react to S an d 123 were retested with T. Twenty-two of the latter group had a posit ive 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 signi ficant. We conclude that in an area where infection with NTM is presen t a simultaneous S test may clarify the meanings of initial and booste r-positive responses to T in the elderly, as well as exclude anergy wh en the T test is negative.