BACKGROUND: QuantiFERON TB-2nd Generation (QFT) is an accurate tool for detecting tuberculosis infection regardless of past history of BCG vaccination. In Japan, QFT test was recognized for diagnostic tool on April 2005, and adopted officially on January 2006. Tuberculosis Society issued Guideline for using QFT-2G on May 2006.
PURPOSE: This article describe the usefulness and remarks in clinical use on diagnosis and system for detection of tuberculosis infection among staff in NHO Tokyo Hospital that has 100 beds for tuberculosis.
METHOD: (1) QFT test for 403 definite diagnosed tuberculosis patient before tuberculosis treatment or within 7 days chemotherapy in NHO Tokyo Hospital. Seventy-four patients have immunosuppressive diseases such as diabetes mellitus, malignant disease, using corticosteroid or immunosuppressor and HIV+ including overlap diseases. QFT result was analyzed by immunosuppressive diseases and by age for 329 patients who have no immunosuppressive diseases. (2) For control of tuberculosis infection of staff, QFT test is used in 3 situation. One is baseline QFT for staff who are shifted to tuberculosis ward from non-tuberculosis ward and new employee, 2nd is following up for staff who work at tuberculosis ward, and 3rd is contact investigation for staff who work at non-tuberculosis ward. Tuberculin skin testing and baseline QFT were done for 92 staff on April 2006, 2 were shifted to tuberculosis ward from non-tuberculosis ward and 90 were new employee.
RESULT: (1) Among 403 definite diagnosed tuberculosis patient before tuberculosis treatment or within 7 days chemotherapy, QFT positive rate was 78.7%. Among 74 patients who have immunosuppressive diseases such as diabetes mellitus, malignant disease, using corticosteroid or immunosuppressor and HIV+ including overlap diseases, QFT positive rate was 58-70%. Among 329 patients who have no immunosuppressive diseases, QFT positive rate was 88-89% in thirties and forties, 69% in sixties and 63% in nineties. QFT-2G test for 134 previously treated tuberculosis cases who are not suffered from active tuberculosis, 49 cases (37%) were positive, 27 cases (20%) were intermediate and 58 cases (43%) were negative. Instructive three cases were reviewed. Suspicion of tuberculosis relapse with QFT negative case was M. avium-intracellulare disease. Suspicion of M. avium-intracellulare disease rather than tuberculosis by X-ray and CT with QFT positive case was tuberculosis. A case with small nodule on CT with QFT positive was adenocarcinoma. (2) Tuberculin Skin Testing and baseline QFT for 92 staff, 4 were QFT positive. Compared with Tuberculin Skin Testing more than 29 mm in erythema, QFT positive rate was 9% and more than 9 mm in induration, QFT positive rate was 7%. By following up QFT test for staff working at tuberculosis ward, 2 staff, one nurse and one helper, were diagnosed tuberculosis infection. As to contact investigation, one nurse was diagnosed tuberculosis infection.
CONCLUSION: Although QFT is a very excellent tool for detecting tuberculosis infection, on clinical diagnosis, it is important to mind that QFT depends on clinical condition especially immunosuppressive diseases, aging and past infection. We cannot diagnose or exclude active tuberculosis by QFT result. This is a useful assistant tool on clinical diagnosis.
