Tuberculosis

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Epidemiology of Tuberculosis
Summary

From 1953 through 1984, the number of TB cases reported in the United States decreased by an average of 6% each year. Since 1985, however, the number of new cases has increased by 14% — from 22,201 in 1985 to 25,313 in 1993. We can attribute the recent increase in TB cases to at least four factors: the HIV epidemic, immigration from countries where TB is common, the spread of TB in certain settings, and inadequate funding for TB control and other public health efforts.

Some groups of people are at higher risk for TB disease because they are more likely to be exposed to or infected with M. tuberculosis. This category includes close contacts of people with infectious TB disease, people born in areas of the world where TB is common, elderly people, low-income groups with poor access to health care, and people who inject illicit drugs. It also includes people who live or work in certain settings (for example, nursing homes, correctional facilities, homeless shelters, and drug treatment centers) and other people who may be exposed to TB on the job, such as health care workers.

Other groups of people are at higher risk for TB disease because they are more likely to develop the disease once infected — for example, people with certain medical conditions, especially HIV infection. For people infected with M. tuberculosis and HIV, the risk of developing TB disease is about 7% to 10% each year. In contrast, for people infected only with M. tuberculosis, the risk of developing TB disease is 10% over a lifetime.

Studies show that there is a connection between the HIV epidemic and the increasing rates of TB. First, the areas that have been the most affected by the HIV epidemic have also reported the largest increases in TB cases. Second, the largest increase in TB cases has occurred among people aged 25 to 44, the age group most affected by AIDS. Third, TB is common among AIDS patients. Fourth, HIV infection is common among TB patients.

More than 70% of TB cases reported in the United States in 1993 were in racial and ethnic minorities. This is probably because a greater proportion of people in these groups have other risk factors for TB.

From 1985 to 1993, the number of TB cases in children increased by 36%. The occurrence of TB disease and infection in children provides important information about the spread of TB in homes and communities. For example, when a child has TB disease or infection, we learn that TB was transmitted relatively recently. This means that the person who transmitted TB to the child may still be infectious. This also means that other adults and children in the household or community have probably been exposed to TB. If they are infected, they may develop TB disease in the future.

published with kind permission of CDC Center for Disease Control http://www.cdc.gov

Atypical TB