[Analysis of tuberculosis infection among foreigners using QuantiFeron TB-2G test]

The purpose of this study was to investigate contacts of a tuberculosis patient among foreigners using QuantiFERON TB-2G (QFT-2G) test.

Three index cases in this study were all foreigners. Contacts, who were mostly foreigners and some Japanese, were investigated by a chest X-ray examination, tuberculin skin test (TST) and QFT-2G, and all data were compared.

Among 48 subjects (30 Vietnamese and 18 Japanese) in case 1, 8 Vietnamese and 2 Japanese were QFT-2G positive. One contacts among 3 most close contacts who lived in the same room with the index case was QFT-2G positive. In case 2, three Chinese among 22 contacts were QFT-2G positive, and a very close contact who lived in the next door to the index case was QFT-2G negative. Seven QFT-2G positive Chinese were identified among 24 contacts in case 3. However, four very close contacts among them were QFT-2G negative.

Although it was unclear whether QFT-2G positives in cases 1 and 2 were infected with M. tuberculosis through the index cases, it is possible to speculate that these QFT-2G positives were already infected with M. tuberculosis while they live in their own country based on the prevalence of TB in their countries and the fact that many very close contacts were QFT-2G negative. Also, it was suggested that QFT-2G positives in case 3 may not be infected through the index case, but infected in their country, since all close contacts were QFT-2G negative. The results of this study suggested that using the QFT-2G test for foreigners prior to or soon after their entry to Japan and recommending chemoprophylaxis for those who are QFT-2G positive would be a very efficient control measures against immigrant foreigners with TB infection.