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T ‐ S pot. TB outperforms tuberculin skin test in predicting development of active tuberculosis among household contacts
Author(s) -
Leung Chi Chiu,
Yam Wing Cheong,
Ho Pak Leung,
Yew Wing Wai,
Chan Chi Kuen,
Law Wing Sze,
Lee Shuk Nor,
Chang Kwok Chiu,
Tai Lai Bun,
Tam Cheuk Ming
Publication year - 2015
Publication title -
respirology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 85
eISSN - 1440-1843
pISSN - 1323-7799
DOI - 10.1111/resp.12483
Subject(s) - medicine , tuberculin , tuberculosis , skin test , asymptomatic , incidence (geometry) , vaccination , tuberculin test , immunology , pathology , physics , optics
Background and Objective In H ong K ong, neonatal B acillus C almette– G uerin ( BCG ) vaccination is practiced with 99% coverage. This study was to compare the performance of T ‐ S pot. TB and tuberculin skin test ( TST ) in predicting tuberculosis ( TB ) among household contacts. Methods From 1 M arch 2006 to 31 J uly 2010, 1049 asymptomatic household contacts of smear‐positive patients were simultaneously tested with T ‐ S pot. TB and TST , and then followed for up to 5 years for development of TB . Attending clinicians and subjects were blinded to the results of T ‐ S pot. TB . Results T ‐ S pot. TB gave a significantly higher positive rate (32.7% vs 22.1%) and better association with exposure time than TST at the 15 mm cut‐off. Agreement between T ‐ S pot. TB and TST using cut‐offs of 5, 10 and 15 mm were relatively poor (kappa 0.25–0.41) irrespective of presence or absence of BCG scar. Only T ‐ S pot. TB positivity was negatively associated with BCG scar. Both T ‐ S pot. TB (incidence rate ratio between test‐positive and test‐negative subjects, IRR : 8.2) and TST ( IRR : 4.1, 6.1 and 2.8, using cut‐offs of 5 mm, 10 mm and 15 mm, respectively) helped to predict TB . Using a TST cut‐off of 15 mm, 56% of future TB cases and 62.5% of bacteriologically confirmed cases were missed. Lowering the TST cut‐off to 10 mm or 5 mm could achieve sensitivity comparable with that of T ‐ S pot. TB , but at the expense of lower specificities, with more positive tests (thus requiring treatment) per case of TB predicted. Conclusions T ‐ S pot. TB outperformed TST in predicting TB among household contacts in a high‐income area with widespread BCG vaccination coverage.