[Timing of quantiferon TB-G test for the contact examination of tuberculosis]

To investigate the timing when Quanti FERON TB-Gold test (QFT-G) for the contact examination of tuberculosis should be done.

We examined QFT-G test for the 25 family contacts of sputum smear positive tuberculosis cases diagnosed at Fukujuji Hospital 5 times (soon after the diagnosis of the index case, 2 months later, 3 months later, 4 months later and 6 months later). And we calculated the positivity at these examinations.

Among 25 contacts, 8 persons became QFT-G positive. The positivity was higher among the contacts of cases with longer delay in diagnosis. 2 contacts were positive soon after the diagnosis of index cases, 5 cases became positive 2 months after the diagnosis and 1 case became positive after 3 months.

3 months interval from the diagnosis of the index case will be enough for the final decision of the infection of contacts.