A new approach based on epidemiological evidence of latent tuberculosis shows that it will be extremely difficult to meet the WHO targets to eliminate tuberculosis by 2035.

2019.08.05 | Af Lars Elgaard Pedersen, AUH

A new study from Aarhus University Hospital and Aarhus University has shown that probably 1 in 4 people in the world carry the tuberculosis bacterium in the body. The disease tuberculosis is caused by the bacterium Mycobacterium Tuberculosis, which affects more than 10 million people every year, and kills up to 2 million, making it the most deadly of the infectious diseases.

In addition, many are infected with the tuberculosis bacterium without having active disease, which is called latent tuberculosis. This number has so far been estimated on the basis of assumptions on how many a patient with active tuberculosis may infect, but there has not been an empirical basis for these assumptions.

Now, researchers from Denmark and Sweden have used a new method to describe the occurrence of latent tuberculosis infection. The researchers have reviewed 88 scientific studies from 36 different countries, and on the basis of this epidemiological evidence they have estimated a prevalence also in those countries where no studies are available, additionally they have calculated the approximate total global prevalence.

- The study emphasizes that it will be extremely difficult to reach the goal of eliminating tuberculosis by 2035, which is the aim of the WHO. At any rate, the objective cannot be achieved without treating the large incidence of latent tuberculosis, since all infected people are at risk of developing active tuberculosis disease later in life, says Christian Wejse, an infectious disease specialist at Aarhus University Hospital and Associate Professor at Aarhus University.

It has previously been estimated that somewhere between one-third and one-fourth have latent tuberculosis, but the new study, which is based on tests from 351,811 individuals, indicates that it is between one-fifth and one-fourth, depending on the test method used. The study thus documents a significant occurrence of tuberculosis infection in the world today, albeit slightly less than previously thought.

Behind the research result:

• Study type: Meta-analysis of population studies on the prevalence of latent tuberculosis, a total of 88 studies from 36 countries with 351,811 participants.
• Partners: Lindköping University, Sweden.
• External funding: The Novo Nordisk Foundation, The Swedish Research Council, The Swedish Heart-Lung Foundation
• Conflicts of interest: None
• Publicering: Cohen A, Mathiasen VD, Schön T, Wejse C. The global prevalence of latent tuberculosis: a systematic review and meta-analysis. Eur Resp J 2019, June 20

Contact:

Specialist in Infectious Diseases and  Associate Professor in Global Health, Christian Wejse
Aarhus University Hospital and  Dept of Public Health, Aarhus University
Tel.: (045) 519 44 519
E-mail: wejse@dadlnet.dk

Fact box

Testing for latent tuberculosis

Latent tuberculosis infection can only be detected indirectly by testing for if the immune system recognizes specific proteins from the tuberculosis bacterium. If there is an immune response, this is taken as an indication that you have been infected and thus the bacteria are "dormant" in the body, or in the process of developing an active infection. Test for latent infection is done either through injecting the proteins into the skin and measuring the redness and swelling of the skin, or by taking a blood sample where the white blood cells are exposed to the tuberculosis proteins for 24 hours, after which the white blood cell secretion of certain signal substances in the blood sample is measured.

Tuberculosis treatment

If you are sick with active tuberculosis, you need treatment for at least 6 months with 4 different kinds of medicine.
If infected with the bacterium, one does not necessarily get sick, but you have so-called latent tuberculosis, and will be at risk of developing active tuberculosis. You can treat latent tuberculosis with antibiotics for 3-4 months.
A new weekly dispensed treatment has just become available and is being tested in Denmark.

You can read more about the research group at:

http://clin.au.dk/en/research/medical-specialities/infectious-diseases/department-q/department-of-infectious-diseases/the-international-center-of-global-infectious-diseases/

http://ph.au.dk/en/research/research-units/global-health/