Self-Study Modules on Tuberculosis
This is an archived document. The links are no longer being updated.
2: Epidemiology of Tuberculosis
Answers To Study Questions
2.1. What happened to the number of TB cases in the United
States between 1953 and 1984?
From 1953 through 1984, the number of TB cases reported in the
United States decreased by an average of 6% each year.
2.2. What happened to the number of TB cases in the United
States between 1985 and 1993?
From 1985 to 1993, the number of new cases increased
2.3. Name four factors that have contributed to the recent
increase in the number of TB cases.
- The HIV epidemic
- Immigration from countries where TB is common
- The spread of TB in certain settings (for example, correctional
facilities and homeless shelters)
- Inadequate funding for TB control and other public health efforts
2.4. Name eight groups of people who are more likely to
be exposed to or infected with M. tuberculosis.
- Close contacts of people with infectious TB
- People born in areas of the world where TB is common (for example,
Asia, Africa, or Latin America)
- Elderly people
- Low-income groups with poor access to health care, including
- People who inject illicit drugs
- People who live or work in residential facilities (for example,
nursing homes or correctional facilities)
- Other people who may be exposed to TB on the job (for example,
some health care workers)
- People in other groups as identified by local public health
2.5. Why is the risk of being exposed to TB higher in certain
settings, such as nursing homes or correctional facilities?
The risk of being exposed to TB is higher in certain
settings because many people in these facilities are at risk for
TB. The risk of exposure to TB is even higher if the facility is
2.6. What are some reasons why rates of TB disease are
higher in correctional facilities?
First, many inmates already have TB infection and therefore
are at higher risk of developing TB disease. Second, an increasing
number of inmates are infected with HIV, which means that they are
more likely to develop TB disease if they become infected with M.
tuberculosis. Finally, some correctional facilities are crowded,
which promotes the spread of TB.
2.7. Name five groups of people who are more likely to
develop TB disease once infected.
- People with HIV infection
- People with other medical conditions that appear to increase
the risk for TB
- People recently infected with M. tuberculosis (within
the past 2 years)
- People with chest x-ray findings suggestive of previous TB disease
- People who inject illicit drugs
2.8. What evidence shows that the HIV epidemic has played
a part in the recent increase in the number of TB cases? Name four
pieces of evidence.
- The areas that have been the most affected by the HIV epidemic
have also reported the largest increases in TB cases.
- The largest increase in TB cases has occurred among people aged
25 to 44, the age group most affected by AIDS.
- TB is common among AIDS patients.
- HIV infection is common among TB patients.
2.9. If a person is infected with both M. tuberculosis
and HIV, what are his or her chances of developing TB disease? How
does this compare to the risk for people who are infected only with
The risk of developing TB disease is about 7% to 10%
each year for people who are infected with both M. tuberculosis
and HIV. In contrast, the risk of developing TB disease is 10% over
a lifetime for people infected only with M. tuberculosis.
2.10. What is the strongest known risk factor for the development
of TB disease?
HIV infection is the strongest known risk factor for
the development of TB disease in people with TB infection. HIV infection
weakens the body's immune system, making it more likely that a person
who has TB infection will develop TB disease.
2.11. Which racial and ethnic groups are disproportionately
affected by TB?
Asians and Pacific Islanders, non-Hispanic blacks, Hispanics,
and American Indians and Alaskan Natives are disproportionately
affected by TB.
2.12. When a child has TB infection or disease, what may
be true about the spread of TB in the child's home or community?
Name three things.
When a child has TB infection or disease, we learn that
- TB was transmitted relatively recently
- The person who transmitted TB to the child may still be infectious
- 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
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
Please send comments/suggestions/requests
CDC/Division of Tuberculosis Elimination
Communications, Education, and Behavioral Studies Branch
1600 Clifton Rd., NE - Mailstop E-10, Atlanta, GA 30333