[Study of the two-step tuberculin tests and gamma-interferon assays in elderly persons]

Recently, an outbreak of lung tuberculosis among elderly residents happened in the home for aged, and it has become a social problem. To analyze the problem of tuberculosis in the elderly persons, we performed two-step tuberculin tests at two weeks interval and gamma-interferon assays for diagnosis of human tuberculosis to residents in the home for aged. 45 males (age; 77.3 +/- 8.9 SD) and 118 females (age; 81.9 +/- 8.6 SD) elderly persons (> or = 60) were examined. Standard dose of PPD was injected intracutaneously, and read at 48 hours. Erythema of 10 mm diameter or more was considered positive. The results were as follows. (1) The percentages of positive reactors in the 1st (T1) and the 2nd (T2) tuberculin tests were 50.3% and 68.1%, respectively. (2) The diameters of erythema and percentage of positive reactors (T1) did not very with age, but the size of erythema increased from 13.5 mm (T1) to 21.2 mm (T2) among those below 80 years, and from 13.0 mm (T1) to 16.4 mm (T2) among those 80 years or higher (p < 0.01). (3) The percentage of positive reactors (T1) varied by sex, namely males react stronger than females. (4) A dose of interferon-gamma released specifically in response to PPD stimulation of whole blood cultures showed no close relation with the diameters of erythema. In conclusion, tuberculin reactivity waned among elderly persons, and the fact suggests that they would have lower resistance against new infections, and as a result, they might have higher risk of developing tuberculosis. Elderly residents should be performed two-step tuberculin tests at the time of their entrance to the home for aged, and negative reactors should carefully be followed up.