Based on data involving more than 80,000 patients, an international research group has developed a programme that can predict the individual risk of tuberculosis. The results of this work were presented on 19 October 2020 in the renowned journal NATURE MEDICINE.
In Germany, an estimated six million people are infected with the tuberculosis pathogen, Mycobacterium tuberculosis, but less than one per cent of these people actually fall ill each year and require treatment. In order to prevent an outbreak of the disease, “latently” infected persons who are identified by standard immunological tests can be treated preventively with antibiotics. The new programme can now calculate how useful this is in individual cases.
“Since immune tests are very poor at predicting the future occurrence of tuberculosis, it would be ineffective to treat all persons with a positive test result with antibiotics as a precautionary measure”, explains Prof. Christoph Lange, Clinical Director at the Borstel Research Centre, scientist at the German Center for Infection Research (DZIF) and co-author of the current study. Preventive antibiotic therapy for tuberculosis is very long-winded, lasting four months, and an antibiotic is not without side effects.
“Investigations must be limited to people in risk groups in order to identify those who are at highest risk of falling ill”, explains Lange. This includes people who are in close contact with tuberculosis patients (especially children), immunocompromised persons and migrants from high-incidence countries. Tuberculosis patients with rheumatoid arthritis, inflammatory bowel disease or psoriasis who are treated with so-called TNF antagonists are another risk group. If the test result is positive, these people should also receive antibiotic therapy as a precautionary measure.
The new “Periscope-TB” programme can now assess the risk of tuberculosis on a case-by-case basis and thus provide physicians in health offices, HIV clinics or preliminary registration centres with the necessary decision-making tool for potential preventive therapy.
For this programme, the international research group led by Dr Rishi Gupta from the University College London collected data from 80,468 people from 20 countries, with information on the incidence of tuberculosis in the coming years after testing with a tuberculin skin test or IGRA. The programme uses key variables to calculate the risk of the future occurrence of tuberculosis in an individual case and the number of people who need preventive antibiotic treatment to curtail a case of tuberculosis.
Tuberculosis is the most common infectious disease leading to death worldwide. Tuberculosis bacteria are transmitted from person to person by droplets coughed out by patients suffering from pulmonary tuberculosis and inhaled by persons in close contact. People who come in close contact with tuberculosis patients, especially young children, immunocompromised persons and people from countries where tuberculosis is common, have an increased risk of contracting tuberculosis. It is estimated that about one in four people worldwide is latently infected, i.e. has tuberculosis bacteria in their bodies; based on current information, however, less than one per cent of those infected are actually symptomatic.
An immunoassay can determine if someone has already been infected with tuberculosis bacteria. These tests cannot detect the infection itself, but they can provide indirect information as to whether the body has produced antibodies that are directed against tuberculosis bacteria or individual components of tuberculosis bacteria. The most commonly used tests are the tuberculin skin test and the so-called interferon-gamma release assay (IGRA). If a person from the above-mentioned risk groups tests positive, the development of active tuberculosis can be prevented by prophylactic treatment with an antibiotic. Antibiotic therapy to prevent tuberculosis lasts 24 times longer than treatment for normal pneumonia.