Questions and Answers About TB
On this Page
- Should I get tested for TB?
- What are the tests for TB infection?
- What if I have a positive test for TB infection?
- What if I have been vaccinated with BCG?
- If I have latent TB infection, how can I keep from developing active TB disease?
- What if I have HIV infection?
- If I was exposed to someone with active TB disease, can I give TB to others?
Latent TB Infection
Should I get tested for TB?
You should get tested for TB if
- You have spent time with a person
known or suspected to have active TB disease; or
- You have HIV infection or another condition that weakens
your immune system and puts you at high risk for active TB
disease; or
- You have symptoms of active TB disease; or
- You are from a country where active TB disease is very
common (most countries in Latin America and the Caribbean,
Africa, Asia, Eastern Europe, and Russia); or
- You live somewhere in the United States where active TB
disease is more common such as a homeless shelter, migrant farm
camp, prison or jail, and some nursing homes; or
- You inject illegal drugs.
What are the tests for TB infection?
The TB skin test
The TB skin test may be
used to find out if you are infected with TB bacteria. You can get a
skin test at the health department or at your doctor's office. A
health care worker will inject a small amount of testing fluid
(called tuberculin or PPD)
just under the skin on the lower part of your arm. After 2 or 3
days, you must return to have your skin test read by the health care
worker. You may have a swelling where the tuberculin was injected.
The health care worker will measure this swelling and tell you if
your reaction to the test is
positive or negative. A
positive reaction usually means that you have been infected by
someone with active TB disease.
If you have recently been infected with TB bacteria, your TB skin test reaction may not be positive yet. You may need a second skin test 8 to 10 weeks after the last time you spent time with the person with active TB disease. This is because it can take several weeks after infection for your immune system to react to the TB skin test. If your reaction to the second test is negative, you probably do not have TB infection.
Special TB blood tests
These are new tests available that use a blood sample to find out if
you are infected with TB bacteria. The tests measure the response of
TB proteins when they are mixed with a small amount of blood. Since
they are relatively new, few health departments offer these blood
tests. If your health department does offer the special TB blood
tests, only one visit is required to draw blood for the test.
Examples of these special TB blood tests include
QuantiFERON®-TB Gold (QFT-G),
QuantiFERON®-TB Gold In-Tube test (QFT-GIT); and T-Spot®.TB test.
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What if I have a positive test for TB
infection?
If you have a positive reaction to the TB skin test, or special TB blood test, your doctor or nurse may do other tests to see if you have active TB disease. These tests usually include a chest x-ray. They may also include a test of the sputum you cough up. Because the TB bacteria may be found somewhere other than your lungs, your doctor or nurse may check your blood or urine, or do other tests. If you have active TB disease, you will need to take medicine to treat the disease.
What if I have been vaccinated with BCG?
BCG is a vaccine for TB. This vaccine is not widely used in the United States, but it is often given to infants and small children in other countries where TB is common. BCG vaccine does not always protect people from getting TB.
If you were vaccinated with BCG, you may have a positive reaction to a TB skin test. This reaction may be due to the BCG vaccine itself or due to infection with the TB bacteria. Your positive reaction is more likely to mean you have been infected with TB bacteria if
- You recently spent time with a person who has active TB disease; or
- You are from an area of the world where active TB disease is very common (such as most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia); or
- You spend time where TB disease is common (homeless shelters, migrant farm camps, drug-treatment centers, health care clinics, jails, prisons).
The special TB blood tests are not affected by prior BCG
vaccination and are less likely to give a false-positive result.
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If I have latent TB
infection, how can I keep from developing active TB disease?
Many people who have latent TB infection never develop active TB disease. But some people who have latent TB infection are more likely to develop active TB disease than others. Those at high risk for active TB disease include
- people with HIV infection
- people who became infected with TB bacteria in the last 2 years
- babies and young children
- people who inject illegal drugs
- people who are sick with other diseases that weaken the immune system
- elderly people
- people who were not treated correctly for TB in the past
If you have latent TB infection (a positive TB skin test reaction
or positive TB blood test) and you are in one of these high-risk
groups, you need to take medicine to keep from developing active TB
disease. This is called treatment for latent TB infection. There are
several treatment options. You and your health care provider must
decide which treatment is best for you.
The medicine usually taken for the treatment of latent TB infection is called isoniazid (INH). Taken for 6 to 9 months, INH kills the TB bacteria that are in the body. If you take your medicine as instructed by your doctor or nurse, it can keep you from developing active TB disease. Children, adolescents, and HIV-infected persons with latent TB infection need to take INH for 9 months.
Because there are less bacteria, treatment for latent TB infection is much easier than treatment for TB disease. Usually, only one drug is needed to treat latent TB infection. A person with active TB disease has a large amount of TB bacteria in the body. Several drugs are needed to treat active TB disease.
Sometimes people are given treatment for latent TB infection even if their skin test reaction is negative. This is often done with infants, children, and HIV-infected persons who have recently spent time with someone with active TB disease. This is because they are at very high risk of developing active TB disease soon after they become infected with TB bacteria.
It is important that you take all the pills as prescribed. If you start taking INH, you will need to see your doctor or nurse on a regular schedule. The doctor or nurse will check on how you are doing. Some people have serious side effects from INH. If you have any of the following side effects, call your doctor or nurse right away:
- no appetite
- nausea
- vomiting
- yellowish skin or eyes
- fever for 3 or more days
- abdominal pain
- tingling in the fingers and toes
| Warning: Frequent or heavy drinking of alcoholic beverages (wine, beer, and liquor) while taking INH can be dangerous. Check with your doctor or nurse for more information. |
People who have latent TB infection need to know the symptoms of
active TB disease. If they develop symptoms of active TB disease,
they should see a doctor right away.
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What if I have HIV infection?
Because HIV infection weakens the immune system, people with latent TB infection and HIV infection are at very high risk of developing active TB disease. All persons with HIV infection should be tested to find out if they have latent TB infection. If they have latent TB infection, they need treatment as soon as possible to prevent them from developing active TB disease. If they have active TB disease, they must take medicine to treat the disease.
Active TB disease can be prevented and treated, even in people
with HIV infection.
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If I was exposed to someone with active TB disease, can I give TB to
others?
If you were exposed to someone with active TB disease, you may become infected with TB bacteria, but you would not be able to spread the bacteria to others right away. Only persons with active TB disease can spread TB to others. Before you would be able to spread TB bacteria to others, you would have to breathe in TB bacteria and become infected. Then the active bacteria would have to multiply in your body and cause active TB disease. At this point, you could possibly spread TB bacteria to others.
Some people develop active TB disease soon (within weeks) after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick years later, when their immune system becomes weak for another reason. Many people with TB infection never develop TB disease.
In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection cannot spread TB bacteria to others. People who have latent TB infection can be treated to prevent developing active TB disease.
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Contact Us:
- Centers for Disease Control and Prevention
Division of Tuberculosis Elimination (DTBE)
1600 Clifton Rd., NE
MS E10
Atlanta, GA 30333 - 800-CDC-INFO
(800-232-4636)
TTY: (888) 232-6348 - New Hours of Operation
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