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

Background: 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. Methods: 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. Results: LTBI prevalence was 37.4% (939/2509). Prevalence was higher in men than women (40.6% versus 33.5%; p < 0.001), and in all age groups, relative to children <5 years (12.2%; p < 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). Conclusions: The LTBI risk in immigrant contacts increases with recent exposure time to the index case, and may suggest recent LTBI in immigrants.