What Increases the Risk for TB?

Some conditions appear to increase the risk that TB infection will progress to disease. The risk may be about 3 times higher (as with diabetes) to more than 100 times higher (as with HIV infection) for people who have these conditions than for those who do not. Some of these conditions are

• Infection with HIV, the virus that causes AIDS

• Injection of illicit drugs

• Recent TB infection (within the past 2 years)

• Chest x-ray findings suggestive of previous TB

• Diabetes mellitus

• Silicosis

• Prolonged therapy with corticosteroids

• Immunosuppressive therapy

• Certain types of cancer (e.g., leukemia, Hodgkin's disease, or cancer of the head and neck)

• Severe kidney disease

• Certain intestinal conditions

• Low body weight (10% or more below ideal)

When the immune system is weakened, the body may not be able to control the multiplication and spread of tubercle bacilli. For this reason, people who are infected with both M. tuberculosis and HIV are much more likely to develop TB disease than people who are infected only with M. tuberculosis. Studies suggest that the risk of developing TB disease is 7% to 10% each year for people who are infected with both M. tuberculosis and HIV, whereas it is 10% over a lifetime for people infected only with M. tuberculosis.

For people with TB infection and no risk factors, the risk is about 10% over a lifetime. For people with TB infection and diabetes, the risk is 3 times as high, or about 30% over a lifetime. For people with TB infection and HIV infection, the risk is about 7% to 10% PER YEAR, a very high risk over a lifetime.

In an HIV-infected person, TB disease can develop in either of two ways. First, a person who has TB infection can become infected with HIV and then develop TB disease as the immune system is weakened. Second, a person who has HIV infection can become infected with M. tuberculosis and then rapidly develop TB disease.