Tuberculosis Infection (latent) and active/suspect cases of tuberculosis are reportable to the Health Unit.
Tuberculosis infection (latent)
The bacteria M. tuberculosis is present in the lungs, but can survive for years in a dormant state. A person with TB infection does not have active disease, is asymptomatic, and is not contagious. TB infection can develop into active disease at any time.
Identification and treatment of TB infection can substantially reduce the risk of development of active TB disease.
Testing |
The goal of testing for TB infection is to identify individuals who are at increased risk for the development of active TB disease, and therefore, would benefit from treatment of TB infection. There are two acceptable tests for identification of TB infection:
Refer to Chapter 4: Diagnosis of Tuberculosis Infection of the Canadian Tuberculosis Standards, 8th edition (2022) for more information or contact the Communicable Disease Control Program. |
Screening and Treatment |
Screening for TB infection should be undertaken only when there is a commitment to treatment or monitoring, should the test results be positive. Treatment for TB infection should be individualized and based on the risk of prior TB exposure and risk of reactivation. Active TB disease must carefully be ruled out prior to starting TB infection treatment. |
Tuberculin Skin Testing (TST)
The TST consists of the intradermal injection of a small amount of purified protein derivative (PPD) from M. tuberculosis bacteria.
In a person who has cell-mediated immunity to these tuberculin antigens, a delayed hypersensitivity reaction will occur within 48 to 72 hours. The reaction will cause localized swelling and will manifest as induration of the skin at the injection site.
The use of TSTs or IGRAs for the diagnosis of active TB disease in adults is not recommended.
Two-Step TST |
A two-step TST is useful for the initial skin testing of adults who are going to be retested periodically (e.g., healthcare workers), due to an elevated risk of exposure. These persons should undergo a two-step TST prior to any exposure to account for the booster effect. This is because the initial TST may elicit an immune response in persons with remote TB infection or prior Bacille Calmette-Guerin (BCG) vaccination. This "booster" immune response results in a greater response if a second TST is administered anytime from a week to more than a year later. The two-step protocol needs to be performed and documented ONCE. Any subsequent TST should be a one-step, regardless of how long it has been since the last TST. A second test should be performed 1 to 4 weeks after the first test using the same materials and techniques to administer and read the TST. The Health Unit offers TSTs to specific populations:
Contact the Vaccine Preventable Diseases (VPD) program at 705-474-1400 or 1-800-563-2808 ext. 5252 or email at vpd@healthunit.ca. |
Contraindications |
Do NOT give a TST to someone who has:
Vaccination with live viruses may interfere with TST reactions. For persons scheduled to receive a TST, testing should be done as follows:
For more information see TST fact sheet Note: If the opportunity to perform TST might be missed, TST should not be delayed for live virus vaccines. TST may be administered before or on the same day as the live-virus immunizations, but at a different site. |
Who can receive a TST |
A TST CAN be given to those who:
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Steps to Conducting a TST:
Step 1: Administering |
Locate and Clean
Prepare
Inject
Teach Client• Do not cover with bandage • Do not scratch site • Perform all normal activities, including showering and bathing, but do not scrub area • Wheal often disappears within 15 minutes Client must return 48 to 72 hours after administration for reading by a trained healthcare professional.
Document:• Date and time of injection • Tuberculin dose, manufacturer, lot number, and expiry date • Site of injection • Person administering the TST MonitorMonitor client for 15 minutes post-injection in case of allergic reaction. Although very rare, be prepared to manage anaphylaxis. |
Step 2: Reading |
Inspect
Palpate
Mark
Measure
Document
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Step 3: Interpreting TST Results |
False-positive reactions:Some persons may react to the TST even though they are not infected with M. tuberculosis. The causes of these false-positive reactions may include, but are not limited to:
False-negative reactions:Some individuals that are infected with M. tuberculosis may not react to the TST. Reasons for this false-negative reaction may include, but are not limited to:
Interpretation of a positive or negative TSTInterpreting a TST result primarily depends on the clinical context. There are multiple dimensions to consider when faced with a positive or negative TST to help decide whether someone is at risk of developing TB disease. These include the pretest probability that the person is truly infected, the individual risk of TB disease, and the ability of the test to identify persons at risk of disease. Refer to Chapter 4: Diagnosis of Tuberculosis Infection of Canadian Tuberculosis Standards, 8th edition for more information. The online TST/IGRA Interpreter interactive algorithm incorporates all three dimensions discussed above and is highly recommended when deciding on TB infection treatment. TB infection and active/suspect cases of TB are reportable to the CDC Program. |
Step 4: Managing a Positive TST |
Management of a positive TST should occur in two distinct steps:
2. Medical Evaluation
TB infection and active/suspect cases of TB are reportable to the CDC program. |
Size of Induration
TST Result | Situation in which a reaction is considered positive: |
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These groups are more at risk of developing TB infection and/or active TB disease. |
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>5 mm |
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>10 mm |
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>15 mm |
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NOTE: A negative TST or IGRA is expected in up to 30% of children with TB and should not be used to exclude diagnosis. Consider consultation with an infectious disease specialist if there are concerns regarding TB in this population.
Regimen | Duration | Dose | Frequency | Common Side Effects |
---|---|---|---|---|
First-line regimens Rifapentine and Isoniazid (3HP) |
3 months (12 doses) |
Isoniazid: 15mg/kg Maximum: 900mg Rifapentine: 10-14.0 kg: 300mg 14.1-25.0 kg: 450mg 25.1-32.0 kg: 600 mg 32.1-49.9 kg: 750 mg ≥50.0 kg: 900mg Maximum: 900mg |
Once weekly | Flu-like reactions, drug interactions |
Rifampin (4R) | 4 months (120 doses) |
10mg/kg Maximum: 600 mg |
Daily | Rash, drug interactions |
Second-line regimen Isoniazid (9H) |
9 months (270 doses) |
5mg/kg Maximum: 300mg |
Daily |
Hepatoxicity, peripheral neuropathy |
Alternative regimens Isoniazid (6H) |
6 months (180 doses) |
5mg/kg Maximum: 300mg |
Daily |
Hepatoxicity, peripheral neuropathy |
Intermittent Isoniazid for 9 months | 9 months (78 doses) |
15 mg/kg Maximum: 900mg |
Twice weekly | Hepatoxicity, peripheral neuropathy |
Isoniazid and Rifampin (3HR) | 3 months (90 doses) |
Isoniazid: 5mg/kg Maximum: 300mg Rifampin: 10mg/kg Maximum: 600mg |
Daily | Hepatoxicity, peripheral neuropathy, drug interactions |