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TB FAQ - TB Infection

How Can I Get Tested for TB?

A TB skin test or a blood test with QuantiFERON TB Gold ® is the only way to find out if you have TB infection. You can get a skin test at the health department or at your doctor's office. You should get tested for TB if:

  • You have spent time with a person with infectious TB
  • You have HIV infection or another condition that puts you at high risk for TB disease
  • You think you might have TB disease
  • You are from a country where TB disease is very common (most countries in Latin America and the Caribbean , Africa , and Asia , except for Japan )
  • You inject drugs
  • You live somewhere in the U.S. where TB disease is common (most homeless shelters, migrant farm camps, prisons and jails, and some nursing homes)

A health care worker can give you the TB skin test. He or she will inject a small amount of testing fluid (called tuberculin) just under the skin on the lower part of your arm. After 2 or 3 days, the health care worker will measure your reaction to the test. You may have a small bump where the tuberculin was injected. The health care worker will tell you if your reaction to the test is positive or negative. A positive reaction usually means that you have TB infection.

If you have a positive reaction to the skin test, your doctor or nurse may do other tests to see if you have TB disease. These tests usually include a chest x-ray and a test of the phlegm you cough up. Because the TB bacteria may be found somewhere besides your lungs, your doctor or nurse may check your blood or urine, or do other tests. If you have TB disease, you will need to take medicine to cure the disease.

If you have recently spent time with someone with infectious TB, your skin test reaction may not be positive yet. You may need a second skin test 10 to 12 weeks after the last time you spent time with the infectious person. This is because it can take several weeks after infection for your immune system to be able to react to the TB skin test. If your reaction to the second test is negative, you probably do not have TB infection.

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What if I Have Been Vaccinated with BCG?

BCG is a vaccine for TB. This vaccine has never been 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 usually protect people from 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 to a real TB infection. But your positive reaction probably means that you have TB infection if:

  • Your skin test reaction is large
  • You were vaccinated many years ago (because the BCG reaction gets smaller over time)
  • You have ever spent time with a person with infectious TB
  • Someone in your family has had TB
  • You are from a country where TB disease is very common (most countries in Latin America and the Caribbean , Africa , and Asia , except for Japan )

QuantiFERON TB Gold ® is specific for TB Infection and is not positive in people who have been vaccinated with BCG.

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If I Have TB Infection, How Can I Keep from Developing TB Disease?

Many people who have TB infection never develop TB disease. But some people who have TB infection are more likely to develop TB disease than others. These people are at high risk for TB disease. They include:

  • People with HIV infection
  • People in close contact with a person who has infectious TB
  • People who became infected with TB bacteria in the last 2 years
  • Babies and young children
  • People who inject drugs
  • People who are sick with other diseases that weaken the immune system
  • Elderly people

If you have TB infection (a positive skin test reaction) and you are in one of these high-risk groups, you need to take medicine to keep from developing TB disease. This kind of treatment is called Treatment for Latent TB Infection.

People who have TB infection but do not receive this treatment need to know the symptoms of TB. If they develop symptoms of TB disease later on, they should see a doctor right away.

The medicine usually used for treatment latent TB infection is a drug called isoniazid or INH. INH kills the TB bacteria that are inactive in the body. If you take your medicine as prescribed, treatment of latent TB infection will keep you from developing TB disease.

Most people must take INH for at least 9 months. An effective alternative regimen that maybe considered is rifampin for 4 months daily.

Sometimes people are given treatment for latent infection even if their skin test reaction is not positive. This is often done with infants, children, and HIV-infected people who have recently spent time with someone with infectious TB disease. This is because they are at very high risk of developing serious TB disease soon after they become infected with TB bacteria and the skin test might be inaccurate in these people.

It is important that you take all the pills prescribed for you so that your treatment therapy is effective. If you start taking INH, you will need to see your doctor or nurse on a regular schedule. He or she will check on how you are doing. Very few people have serious side effects to INH. However, 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 more 3 days
  • Abdominal pain
  • Tingling in the fingers and toes

Warning: Drinking excessive alcoholic beverages (wine, beer, and liquor) while taking INH can be dangerous. Check with your doctor or nurse for more information.

 

What if I Have HIV Infection?

A person can have TB infection for years without any signs of disease. But if that person's immune system gets weak, the infection can quickly turn into TB disease. Also, if a person who has a weak immune system spends time with someone with infectious TB, he or she may become infected with TB bacteria and quickly develop TB disease.

Because HIV infection weakens the immune system, people with TB infection and HIV infection are at very high risk of developing TB disease. All HIV-infected people should be given a TB skin test to find out if they have TB infection. If they have TB infection, they need treatment of latent TB infection as soon as possible to prevent them from developing TB disease. If they have TB disease, they must take medicine to cure the disease.

TB disease can be prevented or cured in people with HIV infection.

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