First outbreak of multi-drug resistant tuberculosis (MDR-TB) in Denmark involving six Danish-born cases

Background: Denmark is a low-incidence country for tuberculosis (TB) and multidrug-resistant (MDR) TB at 5 and 0.05 cases per 100,000 population, respectively. Until 2018, the transmission of MDR-TB was nonexistent except for a few pairwise related family cases. In this study, we describe the first MDR-TB outbreak in Denmark. Methods: On the basis of genotyping of all Mycobacterium tuberculosis (Mtb) culture-positive cases in Denmark spanning 3 decades, 6 molecular- and epidemiologically linked Danish-born cases were identified as the first cluster of an MDR-TB in Denmark. The primary case was diagnosed posthumously in 2010 followed by 5 epidemiologically linked cases from 2018 to 2019. Results and conclusion: Through a combination of routine Mtb genotyping and clinical epidemiological surveillance data, we identified the first Danish MDR-TB outbreak spanning 10 years and were able to disclose the specific transmission pathways in detail, which helped guide the outbreak investigations. The occurrence of an MDR-TB outbreak in a resource-rich low TB incidence setting such as Denmark highlights the importance of a collaborative control system combining classic contact tracing; timely identification of drug-resistant TB through rapid diagnostics; and a close collaboration between clinicians and classical- and molecular epidemiologists for the benefit of TB control.