Tuberculosis is transmitted in close contact from person to person via droplet nuclei (aerosols) containing the pathogen, which patients with infectious pulmonary tuberculosis release, e.g. when coughing. If these are inhaled by another person, an infection (contagion) can occur. If the inhaled tuberculosis bacteria multiply in the lungs, this leads to tuberculosis; this is the case in around 5 - 10% of all infected people. When the human immune system attempts to destroy the infected cells, parts of the lungs are often attacked. This can result in cavities in the lung tissue. These are called caverns, which are often visible on X-rays. These cavities often contain a large number of bacteria that are difficult for the human immune system to reach. When coughing, bacteria from the caverns or other pathologically altered parts of the lungs can be released back into the surrounding air. If these are inhaled by other people, they can infect other people.

Sick people should therefore wear a surgical face mask as long as bacteria are detectable in the sputum. Contact persons can protect themselves with a respirator mask. However, not everyone with tuberculosis is infectious. If no bacteria are detectable in the sputum or an organ other than the lungs is affected (so-called extrapulmonary tuberculosis), there is generally no risk of infection. With effective treatment, patients are often no longer contagious after just a few weeks of effective therapy. People with a latent tuberculous infection are not contagious if a disease has been ruled out.

Your treating doctor or the staff at the public health department can tell you whether there is still a risk of infection.

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