TB is an illness caused by the germ Mycobacterium tuberculosis that usually infects the lungs, but in some cases can spread elsewhere in the body. In most cases, TB germs do not make a person sick because the body’s immune system is able to control the infection. TB germs remain in the person’s body but are inactive and not spreading. People with inactive TB are not sick and cannot spread TB to others.
If a person’s immune system cannot stop the TB germs from growing, they will develop active TB. Active TB can be infectious and can spread to other people if the germs are found in the lungs or airways. TB is spread through the air when a person with active TB coughs, sneezes, or talks and someone else breathes the germ into their lungs. To catch TB, a person must spend a lot of time with someone who is sick with active TB.
Symptoms of active TB can include:
- cough
- blood in sputum
- weight loss
- night sweats
- fever
People who are experiencing these symptoms should see their family doctor.
TB testing
A test can be done to see if you have the TB germ in your body. This test is called a TB skin test. When you have a TB skin test, a small amount of liquid called Tubersol® is injected under the skin on your forearm. Two to three days later, you must return to have your arm checked. If there is a reaction, it will be measured to see if it is considered positive. The TB skin test has been the same for years. Tuberculin has been used for some time in many countries and is a standard test. Tests can be booked at Public Health by calling 1-800-265-7293 ext. 7006.
- TB skin test FAQs
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What is the cost?
There is no fee for the TB skin test for medical purposes. Proper documentation must be brought from the health care provider who is requesting the test. The cost to have a TB skin test for non-medical purposes is $40 per test.
Who should have a TB skin test?
- Anyone recently exposed to someone with active TB
- People with a medical condition or who take medication that affects their immune system (e.g. HIV or diabetes)
- Immigrants, refugees or travellers from areas with high rates of TB
- Staff or residents of health care facilities, homeless shelters, or correctional facilities
- People who live or work in Aboriginal communities with high rates of TB
Who should not have a TB skin test?
You should not have a TB skin test if you:
- Have a reliable history of being TB skin test positive in the past.
- Have a history of active TB in the past or history of treatment for TB in the past.
- Are allergic to any component of the Tubersol ® or vaccines that have the same components as Tubersol ® which includes phenol.
- Have had a live virus vaccine (e.g. MMR, shingles, or chickenpox) less than 4 weeks before the TB skin test is to be given. This is because the live vaccines can reduce the immune response to the TB skin test. A TB skin test can be done on the same day as live vaccines.
- Have had a major viral illness (e.g. mononucleosis, mumps, measles) in the past month. Anyone with the common cold in the past month can receive their TB skin test.
What is a one-step TB skin test?
A one-step TB test requires that you come in for the test, and return 48-72 hours later to have it read. If you arrive more than 72 hours later the test cannot be read, as the result is no longer valid.
What is a two-step TB skin test?
The two-step TB skin test involves a first step and reading as described above, and then it is repeated again, at least 1-4 weeks later if the first TB skin test was negative. This step also requires you to return in 48-72 hours to have it read. If either the first or second step is positive, you will need a medical examination and chest x-ray to be sure you are not sick with active TB. For people who may need to have routine TB screening because of their work or other risk factors, only the initial testing should be a two-step. Once a baseline is established, further TB skin testing should only require one-step.
Developed by the Middlesex-London Health Unit and adapted with permission.
Test results
Positive
A positive TB skin test may mean that you have been infected with the TB germ at some time in your life. Both inactive and active TB can cause a positive TB skin test reaction.
Your healthcare provider will do further tests to make sure you do not have active TB. These tests may include a chest X-ray, bloodwork and/or sputum testing. (Sputum is the “mixture of saliva and mucus coughed up from the respiratory tract.”)
Negative
In general, if a person has a negative TST no further follow-up is required. If you are being tested as part of a potential exposure to someone who has active TB, a second TST test may be recommended.
TB treatment
Active TB
Treatment for active TB can take up to two years (average is 6 months). Up to four different kinds of medications must be taken daily.; You may need to be isolated and stay away from other people for a while so you do not spread TB to others. Medication must be taken in order to get better and to stop the spread of TB to others.
Inactive TB
Your doctor may suggest that you take one or more medications every day for 4 to 9 months to help prevent you from developing active TB in the future. Medication for inactive TB is very important for people who:
- Have any medical condition that affects their immune system or are taking medication that can weaken the immune system (e.g., corticosteroids), or are underweight
- Have been recently exposed to someone with active TB
- Are immigrants, refugees, or travelers from areas with high TB rates
- Work at, or are residents of, health care facilities, homeless shelters, or correctional facilities
Spread of TB
If you are infected with TB and you have a positive TST, you are not infectious. You are only infectious if you go on to develop active TB. If you have no symptoms and you are well, you could be positive and you are safe.
Ninety percent of people exposed to TB do not develop the disease. For adults that do develop the disease, it could be 1-2 years before the infection progresses to active disease and there are signs and symptoms.
You can’t spread TB unless it is in your lungs and you have active disease.
For questions or to book an appointment for a TB skin test, call 1-800-265-7293 ext. 7006 to speak to a public health nurse.