Tuberculosis: A highly contagious infection caused by the bacterium called Mycobacterium tuberculosis. Abbreviated TB. Tubercles (tiny lumps) are a characteristic finding in TB. Diagnosis may be made by skin test, which if positive should will be followed by a chest X-ray to determine the status (active or dormant) of the infection. Tuberculosis is more common in people with immune system problems, such as AIDS, than in the general population. Treatment of active tuberculosis is mandatory by law in the US, and should be available at no cost to the patient through the public health system. It involves a course of antibiotics and vitamins that lasts about six months. It is important to finish the entire treatment, both to prevent reoccurrence and to prevent the development of antibiotic-resistant tuberculosis. Most patients with tuberculosis do not need to be quarantined, but it is sometimes necessary.
Although there are millions of new cases of TB each year, not everyone exposed to the bacterium becomes infected nor does everybody infected with it develop clinical symptoms of TB. A genetic region has been discovered to be associated with clinical TB. People with at least one high-risk copy of this genetic region are ten times more likely to develop TB than normal. The genetic region contains a gene, NRAMP1, that is known to be involved in the susceptibility to leprosy, which is caused by a bacterium related to TB.