Self-Study Modules on Tuberculosis
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2: Epidemiology of Tuberculosis
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
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
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
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.
Cantwell MF, Snider DE, Cauthen GM, Onorato IM. Epidemiology of tuberculosis
in the United States, 1985 through 1992. JAMA. 1994;272:535-539.
Centers for Disease Control and Prevention. Expanded tuberculosis
surveillance and tuberculosis morbidity — United States, 1993. MMWR.
Centers for Disease Control and Prevention. Tuberculosis morbidity
— United States, 1992. MMWR. 1993;42(36):696-697, 703-704.
Reported Tuberculosis in the United States, 1993. Atlanta,
Ga: Centers for Disease Control and Prevention; 1994.
Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb
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CDC/Division of Tuberculosis Elimination
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