Tuberculosis is a contagious disease caused by the bacteria Mycobacterium Tuberculosis and other bacterium species. It is spread by airborne particles released when someone with active disease coughs, sneezes, or talks. These particles are inhaled by another person who may then become infected. Latent infection occurs when an individual becomes infected with the TB bacillus but does not become acutely ill. Most people’s immune system will prevent the bacteria from multiplying and causing active disease. Without medication, about 10% of those infected will go on to develop actual active disease.

Latent infection = bacteria has entered the body but the immune system has prevented it from developing into active disease. These people are not contagious.

Active disease = most commonly affects the lungs and respiratory system but can infect other organs. The infected person becomes ill and produces phlegm. These people are contageous.

What is the TB test?

The skin test is commonly called a PPD and is performed by injecting a small amount of a Purified Protein Derivative of inactivated tuberculosis bacteria under the skin of the forearm.

• You must return in 48-72 hours after injection to have the area checked.
• A negative test results when there is no redness or swelling at the site of injection.
• A positive test results when there is a certain degree of redness, swelling, and hardness at the site of injection.

Note: The TB skin test does not make you get TB. The TB skin test is not a vaccine to prevent TB.

What does a positive test mean?

• A positive test indicates you have been infected with the TB bacterium at some point in the past.
• It does not necessarily mean you have active, contagious disease.
• You should be evaluated to be sure that you do not have active disease and whether preventive medication is indicated. Evaluation includes a clinical examination and consultation, chest x-ray, and blood work.

What if I have active, contagious disease?

If you are found to have active disease, appropriate medication can generally cure tuberculosis. However, it is imperative that you take the medication and receive medical follow-up because of the contagious and serious nature of the disease. Symptoms may mimic other flu-like illnesses.

What if I have a positive skin test and no disease?

Depending on several variables, preventive therapy may be recommended for you. This includes treatment for 6-12 months with appropriate drug treatment. Proper preventive treatment virtually eliminates the development of active disease sometime later in your life.

What if I had BCG vaccine?

Many countries, particularly in Asia and Africa, give a tuberculosis vaccine called BCG. This is somewhat effective in preventing active disease in countries where the disease is common. BCG vaccine will sometimes cause a positive skin test, but this tends to wane over time. Anybody who is found to have a positive TB skin test, whether or not they have had BCG vaccine, should discuss preventive therapy with their clinician.

Who should get a TB skin test?

Everyone should have a TB skin test at least once to know whether the reaction was positive or negative. You should also be tested if there is any chance you have been around a person who has TB disease or if someone in your family has had TB disease.

You should be tested more often if you are at high risk for TB infection.

If you have HIV infection, it is very important to get tested for TB infection at least once a year.

Other people at high risk include:

• People with medical conditions that increase the risk of TB (such as diabetes, silicosis, leukemias, lymphomas, chronic renal failure or people undergoing treatment with drugs that affect the body’s immune system, such as long-term use of corticosteroids).
• People from countries where TB disease is very common.
• People who do not get medical care, especially in low-income communities.
• People who work in or are residents of long-term care facilities such as nursing homes, prisons, and some hospitals.
• People who are very underweight.
• Alcoholics and persons who inject drugs. All health-care workers and trainers should be tested regularly because of risks to themselves and patients.