Tuberculosis (TB) is a bacterial disease caused by Mycobacterium tuberculosis, an organism belonging to the M. tuberculosis complex, which also includes other genetically related mycobacteria.
M. tuberculosis mycobacteria need to be distinguished from nontuberculous mycobacteria (NTM), which are widely distributed in the environment (soil, water) and can sometimes cause disease but are not transmitted from human to human. Using modern molecular techniques, more than 150 different species of NTM have now been identified. Epidemiological data from some industrialised countries suggest that cases of disease due to NTM are increasing and that NTM disease may even exceed the incidence of TB in countries in which TB incidence is low. The most important NTM is M. avium , which can particularly cause disease in patients with HIV/ AIDS; in total, however, more than 40 NTM species have been reported to cause pulmonary disease, mostly in patients with impaired immune systems or an underlying lung disease, such as chronic obstructive pulmonary disease (COPD), bronchiectasis or cystic fibrosis. These organisms are generally less susceptible to antibiotics than M. tuberculosis, and the decision to treat an individual with a long-term combination of antibiotics depends upon the clinical picture and the causative NTM. Cervical lymphadenopathy (swollen lymph nodes in the neck) caused by M. avium complex is the prevailing manifestation in HIV-negative children, and surgical removal of the nodes is the treatment of choice, combined with antibiotics where necessary.
TB is an important clinical and public health problem worldwide. Although its incidence and prevalence have declined notably in high-income countries over the past century, they have increased in low- and middle-income countries, owing to the emergence of strains resistant to several antimycobacterial drugs and to co-infection with HIV/AIDS.