Surveillance of Employees of Swiss Federal Asylum Centres for Latent Tuberculosis Infection.

BACKGROUND: Asylum seekers in Switzerland have to register in federal asylum centres (FACs) before formal permission to enter the country. Some of them may have active tuberculosis (TB), exposing fellow refugees and employees. OBJECTIVES: The aim of this study was to assess the risk of TB infection among employees of Swiss FACs. METHODS: Between 2010 and 2018, a free interferon-gamma release assay (IGRA) was offered to all employees of 8 FACs, at employment and at yearly intervals. We defined latent TB infection as IGRA conversion from negative to positive. IGRA-positive employees were referred to a medical centre for further clinical follow-up. RESULTS: 1,427 tests were performed among 737 employees (54.6% male). 403 (55%) persons were tested only once; 330 (44.5%) were tested several times; for 4 (0.5%) persons, the number of IGRA tests is unknown. Twenty employees (2.7%) had a positive IGRA at baseline, 2 (0.6%) converted from negative to positive during follow-up, resulting in an incidence of 22/10,000 person-years. We observed no case of active TB among employees. CONCLUSIONS: The prevalence of latent TB among employees to Swiss FACs and the risk of acquiring TB infection through work-related exposure are low. Yearly IGRA controls in the absence of documented TB exposure seem unnecessary.