Tuberculosis outbreak in Eastern Norway.

Background: Tuberculosis is a rare disease in Norway, especially among those who are born here. Contact tracing for cases of pulmonary tuberculosis is essential to find others who are ill or infected, and to prevent further infection. This article describes the investigation of an outbreak in which many of those infected or ill were Norwegian adolescents.
Material and Method: Nine persons directly or indirectly associated with the same educational institution were diagnosed with tuberculosis in 2013. Genetic testing of tuberculosis bacteria linked a further 13 cases of the disease reported in Eastern Norway during the period 2009-2013 to the outbreak. Information from the Norwegian Surveillance System for Communicable Diseases (MSIS) was used to investigate the outbreak, and information was also retrieved on exposure and contact networks.
Results: The first patient at the educational institution had long-term symptoms before diagnosis. Contact tracing for this case included 319 persons, of whom eight were ill, 49 infected and 37 received preventive therapy. The extent of contract tracing for the remaining 21 cases varied and included a total of 313 persons, of whom two were found to be ill (included in the 21 cases), 30 were infected and 12 received preventive therapy.
Interpretation: 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.