Positivity of interferon-gamma release assay among foreign-born individuals, Tokyo, Japan, 2015-2017.

Background: The aim of this study is to analyze interferon-gamma release assay (IGRA) data of foreign-born individuals in Japan derived from tuberculosis (TB) contact investigations. Methods: A contact with a TB patient was considered to have occurred when an individual had contact with a TB patient for more than 8 h indoors. This is a retrospective cohort study, and all the TB contacts tested with IGRA during the contact investigations conducted by the Shinjuku city Health Office from 2015 through 2017 were enrolled. Results: A total of 880 foreign-born contacts were investigated. The IGRA positivity of the contacts from China and Viet Nam were both 5.1% (95% confidence intervals [CIs]: 3.2%-7.8% and 2.4%-9.5%, respectively), whereas that from Nepal and Myanmar were 24.4% (95% CI: 16.0%-34.6%) and 23.3% (95% CI: 9.9%-42.3%), respectively. Multiple logistic regression analysis showed that the risk factors were smear status of the index patient (1+: adjusted odds ratio [aOR]: 6.2, 95% CI: 1.2-30.5, smear status 3+: aOR: 14.3, 95% CI: 1.7-118.2), age of the contact (aOR: 1.1, 95% CI: 1.0-1.1 for 1 year increment), and being born in Nepal (aOR: 5.6, 95% CI: 2.8-11.2) and Myanmar (aOR: 4.3, 95% CI: 1.4-13.0), compared with China as reference. Conclusions: In contact investigations involving foreign-born individuals, local health offices should carefully consider the composition of the TB contacts and expand the focus of the investigation, if deemed necessary.