Tuberculosis: causes, course, diagnosis, treatment and public health

Worldwide

About one third of the world's population is infected with tuberculosis pathogens. However, only a small proportion of infections lead to disease. According to the WHO tuberculosis report (Global tuberculosis report 2016), there were 10.4 million new infections and 1.8 million deaths worldwide in 2015. Both figures have been falling steadily since 1990.

Treatment options are often inadequate, as they require expensive antibiotics, take a long time and are often impracticable given the social circumstances of those affected. Laboratories for diagnosis and treatment are also often lacking in affected regions. In Eastern Europe in particular, poverty and deficiencies in the health system have led to a worrying increase in tuberculosis, especially with multi-resistant strains of the pathogen. Worldwide, too, the disease is increasingly being caused by such drug-resistant tuberculosis strains.

Tuberculosis infection is particularly problematic in HIV-infected persons with manifest AIDS. Due to the immunodeficiency, HIV increases the probability of the outbreak of a tuberculosis disease many times over. In Africa, tuberculosis is the most common cause of death along with AIDS. Both diseases occur in close correlation with each other, especially among inhabitants of metropolitan slums. In this context, immunodeficiency due to HIV often leads to negative results in routine tuberculosis tests, although the disease is present (see also errors of the 1st and 2nd kind). This is due to the fact that the skin tests (tuberculin test, Tine test) check the immunological reaction to pathogen components, but this is inhibited by AIDS. The course of tuberculosis is then considerably accelerated. In poor countries, TB is considered a sign of the onset of AIDS and leads to death in the majority of HIV patients. The WHO therefore calls for and promotes worldwide coordination of tuberculosis and AIDS research.

Surprisingly, an Italian study found a prevalence (disease frequency) of latent tuberculosis infections of nine percent among healthy health care workers and 18 percent among just over 400 people suffering from psoriasis. Also 30 percent of the sick with pneumonia and lung cancer were latently infected.

Germany, Austria and Switzerland

In 2016, 5915 tuberculosis patients were reported to the Robert Koch Institute (RKI) in Germany, including 233 children under the age of 15 (2005: 230). In 2016, there were 7.2 cases per 100,000 inhabitants in Germany. Official statistics gave 100 deaths in 2015. The data probably do not quite correspond to the real figures, as the number of unreported cases of this disease is relatively high due to its non-specific symptoms. According to a pathology study from Germany, only one third of post-mortem tuberculosis cases were diagnosed during life.

In Germany, the disease is particularly prevalent in Hamburg, Bremen and Berlin. Among people born in the country, the older age groups predominate due to the tendency to activation and reactivation as a result of the declining immune defence. Among migrants, the middle age cohorts predominate, as fresh infections are more likely to trigger the disease here. The preliminary tuberculosis statistics for 2017 show a plateau in Germany at the level of 2016, after an increase in tuberculosis cases due to increased immigration in autumn 2015. In Switzerland and Austria, the number of cases also decreased slightly in 2017. A feared stronger increase in the number of cases due to the wave of migration in 2017 has therefore not yet occurred.

In Austria, 583 cases of tuberculosis were recorded in 2015, while Switzerland recorded 546 cases in the same year.

The following table shows the number of new cases per 100,000 inhabitants (incidence) and the number of new cases per year in Germany (D), Switzerland (CH) and Austria (A).

 * contagious only ** provisional figures

The main causative agent of tuberculosis, Mycobacterium tuberculosis, is an aerobic gram-positive rod bacterium that divides every 16 to 20 hours. Compared to other bacteria that have division rates in the range of minutes, this is extremely slow. Microscopic detection is successful due to the typical staining characteristics: The bacterium retains its staining after treatment with an acidic solution and is therefore called an acid-fast rod. In the most common stain of this type, the Ziehl-Neelsen stain, the red stained germs stand out against a blue background. Detection is also possible by fluorescence microscopy and by auramine-rhodamine staining. In the Gram stain, mycobacteria hardly present themselves, but the structure of the peptidoglycan strongly resembles that of Gram-positive bacteria, so that M. tuberculosis is formally classified as Gram-positive. This was confirmed by sequence analyses of the RNA.

The same group of bacteria includes other mycobacteria, which are also counted among the causative agents of tuberculosis: M. bovis, M. africanum and M. microti. These pathogens are found only sporadically in tuberculous diseases in Germany. M. kansasii and also M. avium can in rare cases, like a number of other mycobacteria, cause tuberculosis-like clinical pictures. However, atypical mycobacteria other than tuberculosis (MOTT) do not usually pose a risk of infection.

M. tuberculosis, M. bovis, M. africanum, M. microti, M. canetti, M. pinnipedi, M. caprae and the vaccine strain Bacillus Calmette-Guérin (BCG) are grouped together as the Mycobacterium tuberculosis complex.