On average, 10 million people develop active TB every year (10 million in 2019, according to the World Health Organization (WHO)). TB is one of the top ten causes of death worldwide. In 2019, 1.4 million people died from the disease, 208,000 of whom were also coinfected with HIV. Over 95% of TB deaths occur in developing countries, but tuberculosis is still a major public health problem in many industrialized countries, particularly with multidrug-resistant forms, which are especially difficult and take a long time to treat (> 2 years).
About one-quarter of the world's population is currently infected with Mycobacterium tuberculosis, and just 30 countries account for 87% of all cases worldwide. The number of multidrug-resistant TB cases at global level was estimated at 206,030 in 2019, 10% more than in 2018.
In France, the average incidence of cases is low but French Guiana, Mayotte and Île-de-France (Greater Paris) are the regions with the highest rates (source: Santé publique France).
TB is a contagious disease caused by Koch's bacillus (strains of the Mycobacterium tuberculosis complex). This infectious agent is spread through the air via bacteria-laden droplets produced when TB patients cough. Individuals can be infected by inhaling just a few of these contaminated droplets. A person with active but untreated TB can infect an average of 5 to 15 people a year. Poor health and social conditions are often associated with the spread of the disease.
The active development of the disease among people infected by Koch's bacillus depends on a number of genetic, immunological, nutritional and social factors. It is thought that 5 to 15% of infected people will progress to active TB in their lifetime. The bacillus can survive in a dormant state in the human body for years. Immunodeficient patients are at greater risk of developing active TB. HIV and Koch's bacillus form a lethal combination, as immune system deficiencies caused by HIV infection facilitate progression of TB disease. Among people living with HIV, untreated TB is fatal in almost all cases.
In the 1940s, there were no drugs available to treat TB. Today a combination of antibiotics and chemotherapy drugs is used to treat the disease, but the treatment must be taken for at least six months (and up to two years in multiresistant strains). Incomplete or erratic treatment often causes antibiotic-resistant TB, which can then spread among the community. If treatable, these resistant TB cases are a hundred times more costly than those that can be treated using conventional therapy regimens.
New weapons to fight bacteria
The BCG (Bacillus Calmette-Guérin) vaccine is the only vaccine currently licensed to immunize against TB. Nevertheless, this vaccine which marks its 100th anniversary this year (in 2021) is only partly effective: although it is very useful for preventing severe forms of TB in young children (it is almost 90% effective against tuberculous meningitis), it provides little protection against pulmonary tuberculosis in adolescents and adults, and hence cannot prevent transmission of the disease or eradicate the global epidemic.