Post-screening risk of tuberculosis progression: a three-year retrospective cohort study of asylum seekers in Sweden.

Introduction: Strategies for tuberculosis (TB) elimination in low-incidence countries involve screening recent migrants from TB-endemic regions for TB infection (TBI) and providing TB preventive treatment (TPT) to individuals with an increased risk of reactivation. This study aimed to determine TB incidence and identify reactivation risk markers in a cohort of asylum seekers in Sweden after screening.

Method: We conducted a registry-based retrospective cohort study with a three-year follow-up of asylum seekers receiving post-arrival Interferon Gamma Release Assay (IGRA) screening in three Swedish regions 2015-2019. Medical records, health-examination records, and the national TB disease registry were linked using identification numbers or probabilistic methods. The primary outcome was TB disease more than 90 days post-screening. Explanatory variables included age, sex, IGRA-result (positive/negative), TPT-initiation, and TB incidence in the country of origin. Poisson and Cox regression addressed incidence rates (IR), incidence rate ratios (IRR), and hazard ratios over a three-year follow-up.

Results: The cohort included 21 739 individuals and 70 467 person-years. Incident TB disease was recorded in 41 cases (IR 58.2/100 000 person-years). The IR for those with a positive IGRA was 321.7/100 000 person-years (n = 34). The highest risk was in persons aged under 20 with no TPT (1 279.0/100 000 person-years). Positive IGRA result, age under 20 years, and origin from TB-endemic country predicted incident TB.

Discussion: Risk markers for incident TB were similar to findings previously reported. However, the observed 0.3% annual reactivation risk found among all IGRA-positive individuals in this study was considerably lower compared to earlier findings.