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.

School based screening for tuberculosis infection in Norway: comparison of positive tuberculin skin test with interferon-gamma release assay

Background

In Norway, screening for tuberculosis infection by tuberculin skin test (TST) has been offered for several decades to all children in 9th grade of school, prior to BCG-vaccination. The incidence of tuberculosis in Norway is low and infection with M. tuberculosis is considered rare. QuantiFERON^®TB Gold (QFT) is a new and specific blood test for tuberculosis infection. So far, there have been few reports of QFT used in screening of predominantly unexposed, healthy, TST-positive children, including first and second generation immigrants. In order to evaluate the current TST screening and BCG-vaccination programme we aimed to (1) measure the prevalence of QFT positivity among TST positive children identified in the school based screening, and (2) measure the association between demographic and clinical risk factors for tuberculosis infection and QFT positivity.

Methods

This cross-sectional multi-centre study was conducted during the school year 2005–6 and the TST positive children were recruited from seven public hospitals covering rural and urban areas in Norway. Participation included a QFT test and a questionnaire regarding demographic and clinical risk factors for latent infection. All positive QFT results were confirmed by re-analysis of the same plasma sample. If the confirmatory test was negative the result was reported as non-conclusive and the participant was offered a new test.

Results

Among 511 TST positive children only 9% (44) had a confirmed positive QFT result. QFT positivity was associated with larger TST induration, origin outside Western countries and known exposure to tuberculosis. Most children (79%) had TST reactions in the range of 6–14 mm; 5% of these were QFT positive. Discrepant results between the tests were common even for TST reactions above 15 mm, as only 22 % had a positive QFT.

Conclusion

The results support the assumption that factors other than tuberculosis infection are widely contributing to positive TST results in this group and indicate the improved specificity of QFT for latent tuberculosis. Our study suggests a very low prevalence of latent tuberculosis infection among 9th grade school children in Norway. The result will inform the discussion in Norway of the usefulness of the current TST screening and BCG-policy.