Tuberculosis risk factors

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

Overview

Progression from TB infection to TB disease occurs when the TB bacilli overcome the immune system defenses and begin to multiply.

Risk Factors

In primary TB disease—1 to 5% of cases—this occurs soon after infection. However, in the majority of cases, a latent infection occurs that has no obvious symptoms. These dormant bacilli can produce tuberculosis in 2 to 23% of these latent cases, often many years after infection. The risk of reactivation increases with immunosuppression, such as that caused by infection with HIV. In patients co-infected with HIV, the risk of reactivation increases to 10% per year.

Other conditions that increase risk include drug injection, mainly due to the lifestyle of IV drug users; recent TB infection or a history of inadequately treated TB; chest X-ray suggestive of previous TB, showing fibrotic lesions and nodules; diabetes mellitus; silicosis; prolonged corticosteroid therapy and other immunosuppressive therapy; head and neck cancers; hematologic and reticuloendothelial diseases, such as leukemia and hodgkin's disease; end-stage kidney disease; intestinal bypass or gastrectomy; chronic malabsorption syndromes; or low body weight.

Some drugs, including rheumatoid arthritis drugs that work by blocking tumor necrosis factor-alpha (an inflammation-causing cytokine), raise the risk of activating a latent infection due to the importance of this cytokine in the immune defense against TB.

Twin studies in the 1950's showed that the course of TB infection was highly dependent on the genetics of the patient. At that time, it was rare that one identical twin would die and the other live.