Sweden and Finland are more successful in the fight against tuberculosis than Denmark

The number of tuberculosis cases among Swedish and Finnish indigenous citizens falls faster than in Denmark shows a new Nordic survey.

In Denmark, there is still a high rate of on-going tuberculosis transmission, especially among socially disadvantaged parts of the Danish population. Every year, between 300 and 400 new cases of tuberculosis are registered in Denmark. The majority of patients are born in countries where tuberculosis is far more prevalent than at home, and many may have been infected with the tuberculosis bacteria before entering the country. But also native Danes get tuberculosis.

Now, a new study comparing the trend in tuberculosis rates among native citizens in Denmark, Sweden and Finland shows that it is faster in Sweden and Finland to reduce the number of tuberculosis cases in this group. The study has just been published in the international journal Clinical Microbology and Infection.

In the period 1990-2015, the incidence of tuberculosis among Danish indigenous people decreased by an average of 2.4% a year. In Sweden, the decline was 6.1% annually and in Finland 6.9%.

Udviklingen i tuberkulose i Danmark Sverige og Finland

Yearly number of tuberculosis cases per 100.000 among natives in Denmark, Sweden and Finland on a logarithmic scale. m is the slope and corresponds to the annual rate of change in percent.

Thus, in 2013, Sweden, as the first of the three Nordic countries in the study, reached the WHO level of pre-elimination of tuberculosis for the native group of citizens in the country. For pre-elimination, you understand one yearly new tuberculosis case per 100,000. By comparison, Denmark was 2.0 in 2015 and Finland was 3.2 tuberculosis cases per year. 100,000 among indigenous citizens.

"Compared to neighboring countries Sweden and Finland, Denmark is less efficient in fighting tuberculosis among indigenous citizens. If it continues, as it is now, Denmark will first eradicate tuberculosis among native citizens about 20 years later than Finland. There is a significant difference, "says Director, Consultant, DMSc. Troels Lillebaek, International Reference Laboratory of Mycobacteriology (IRLM), Statens Serum Institut, who, together with MD, PhD-student Mathias Klok Pedersen and Consultant, PhD. Erik Svensson from IRLM, State Serum Institute, is one of the researchers behind the study.

Difference in age of infected persons

The study also showed that there is a big difference in the age distribution of native tuberculosis cases in the three countries. In Sweden and especially in Finland, the majority of those infected are over 65, while in Denmark they are much younger:

"In both Sweden and especially in Finland, most native tuberculosis patients are over 65 years, suggesting they have been infected with tuberculosis bacteria many years ago when tuberculosis was much more common. In Sweden and Finland, the infected persons will then disappear from the statistics over time, while there will still be new tuberculosis cases in Denmark. In Denmark, there are far more cases between 25 and 55 years, indicating that they have been infected recently. That Denmark has a higher level of active tuberculosis transmission is confirmed by our analysis of the DNA profile of the bacteria." Says MD Mathias Klok Pedersen, who has worked with the data in connection with his PhD project.

The Danes are infected with the same bacterial strain When a patient in Denmark is found to have tuberculosis, the bacteria are analyzed at the State Serum Institute, where samples from all Danish tuberculosis patients have been systematically stored since 1992. By analyzing the DNA of the bacteria closer, researchers can see if the bacteria from the tuberculosis patients are completely different - or if they are part of the same chain of transmission. Here too, there are differences between countries. In Denmark, there are far more tuberculosis cases in transmission chains, and especially a chain of transmission is very dominant. In this transmission chain, around 1,000 cases of tuberculosis have been found since 1992.

"There is more active transmission of tuberculosis in Denmark than in other Nordic countries. The fact that so many tuberculosis patients in Denmark are infected with the same tuberculosis strain is an expression of ongoing active spread of tuberculosis in the society. Our results indirectly suggest that there is less effective tuberculosis control in Denmark than in the other Nordic countries, "says Troels Lillebaek.

Tuberculosis affects especially vulnerable people

When finding a patient with tuberculosis, you always have to look for the source of infection and other people who are infected with the bacteria or have developed tuberculosis. Studies have shown that tuberculosis in Denmark especially affects socially disadvantaged. In a screening project among socially disadvantaged persons in Copenhagen, a surprisingly high number of tuberculosis patients has been found. Therefore, this screening is now routinely performed among socially disadvantaged persons in Copenhagen.

"It has been possible to identify many tuberculosis cases among socially disadvantaged in Copenhagen area early in the course of the disease. This has resulted in faster, correct treatment for the benefit of the individual, and less spread of infection, for the benefit of society, as tuberculosis does not spread when the patient is treated. In view of the good results from the Copenhagen area, there are good opportunities for improving tuberculosis control in Denmark. About 40% of tuberculosis cases occur outside of Copenhagen, where there is still no systematic screening activity", says Troels Lillebaek.

The study was conducted in collaboration between the Statens Serum Institute and Rigshospitalet (National Hospital) in Denmark and colleagues from the Swedish Public Health Authority and the Institute for Health and Welfare in Finland.

Read the scientific paper in Clinical Microbiology and Infection:

Trends and differences in tuberculosis incidences and clustering among natives in Denmark, Sweden and Finland – a comparison of native incidences and molecular epidemiology among three low incidence countries (Requires subscription)

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Contact

International Reference Laboratory of Mycobacteriology
Troels Lillebæk 
Director, Consultant, DMSc, DTM&H

Tel: +45 3268 3704