Within 1 week in April 2013, three cases of pulmonary tuberculosis (TB) were reported among students attending training sessions at an educational institution in Oslo, Norway. By the end of October 2013, a total of nine epidemiologically linked cases had been reported. The outbreak encompassed a total of 24 cases from 2009 to 2014, among which all of the 22 Mycobacterium tuberculosis isolates available had identical mycobacterial interspersed repetitive-unitvariable-number tandem-repeat (MIRU-VNTR) profiles (MtbC15-9 code 10287-189) belonging to the Beijing lineage. Whole-genome sequencing (WGS) of the M. tuberculosis isolates revealed 20 variable nucleotide positions within the cluster, indicating a clonal outbreak. The most likely index case was identified and diagnosed in Norway in 2009 but was born in Asia. WGS analyses verified that all of the cases were indeed part of a single transmission chain. However, even when combining WGS and intensified contact tracing, we were unable to fully reconstruct the TB transmission events.

No abstract

Delayed diagnosis led to an unusually large tuberculosis outbreak in a Norwegian context. The extent of contact tracing varied with no obvious relation to the infectiousness of the index patient. The outbreak demonstrates the importance of continued vigilance with regard to tuberculosis as a differential diagnosis, also among patients born in Norway.