Exposure Time to a Tuberculosis Index Case as a Marker of Infection in Immigrant Populations

<b>Background</b>: Exposure time to a tuberculosis (TB) index case may be a marker of a recent latent tuberculosis infection (LTBI) risk. The aim of this study was to determine the LTBI risk involved in immigrant contact based on exposure time to pulmonary TB index cases. <b>Methods</b>: We conducted a 30-month LTBI prevalence study of pulmonary TB immigrant contacts in Catalonia (1 January 2019-30 June 2021). Contacts with LTBI were identified by means of the tuberculin skin test and/or interferon gamma release assay. Variables associated with LTBI in contacts were analysed using adjusted OR (aOR) and 95% confidence interval (CI) values. <b>Results</b>: LTBI prevalence was 37.4% (939/2509). Prevalence was higher in men than women (40.6% versus 33.5%; <i>p</i> < 0.001), and in all age groups, relative to children <5 years (12.2%; <i>p</i> < 0.001)). Prevalence increased with exposure time to the index case; relative to <6 h/week exposure, LTBI risk was greater for both ≥6 h/day (aOR = 2.0; 95% CI: 1.5-2.6) and <6 h/day but ≥6 h/week (aOR = 1.6; 95% CI: 1.1-2.2). <b>Conclusions</b>: The LTBI risk in immigrant contacts increases with recent exposure time to the index case, and may suggest recent LTBI in immigrants.