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Tuberculosis (TB): For health professionals

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Key information

TB is a serious but preventable and treatable infectious disease caused by the bacteria Mycobacterium tuberculosis (MTB). It is the leading cause of death for infectious diseases worldwide and is still present in Canada. While anyone can get TB, it disproportionately impacts people born outside of Canada and Inuit, First Nations and Métis populations.

TB can be diagnosed late or misdiagnosed as it has similar symptoms to other diseases and is not common in many parts of Canada.

Early testing, detection and treatment save lives and helps prevent the spread of TB.

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Disease progression

When MTB are inhaled, they enter the lungs and are taken up by immune cells (alveolar macrophages). Once a person is infected, their outcomes may vary based on a combination of the following factors.

  • Cleared infection: Some individuals with a healthy immune system will clear the bacteria and have negative test results.
  • TB infection: Some individuals will contain the infection, and keep it in a dormant state and not pass it on to others. People with TB infection may progress to TB disease at any time, even years to decades later.
    • An estimated 5% to 10% infected with MTB will develop TB disease during their lifetime, with the highest risk in the first 2 years after exposure.
  • Asymptomatic (subclinical) TB: Some individuals may develop TB disease without symptoms, but it can be detected on microbiological tests or imaging.
    • Asymptomatic TB is likely transmissible and public health guidance on detection and treatment is currently being reviewed.
  • TB disease: Individuals have symptoms.
    • Those with pulmonary and laryngeal TB disease can pass it on to others after prolonged contact.

Some factors that significantly increase the risk of progressing to TB disease include:

  • close contact with a person with contagious TB disease
  • age (infants, children under 5, and older adults)
  • human immunodeficiency virus (HIV), diabetes, kidney disease and dialysis, cancer, and silicosis
  • immune suppressing medications and disorders
  • smoking and substance use (including alcohol and injection drug use)

The most effective way to reduce transmission is to promptly diagnose, isolate and treat patients with TB disease.

TB is a notifiable disease in every Canadian province and territory. This means that cases must be reported to the corresponding provincial and territorial department of health.

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Signs and symptoms of TB disease

Signs and symptoms of TB disease depend on where the infection is located in the body. Pulmonary TB is the most common site of TB disease. However, TB can infect any site including extrapulmonary infections of the brain, bones, abdomen, and lymph nodes and other sites.

Extrapulmonary TB disease may present with systemic signs like fever, and symptoms specific to the site of infection. For example:

  • TB meningitis (headache, confusion)
  • spinal TB (back pain)
  • gastrointestinal TB (chronic abdominal pain, weight loss, mass on imaging)
  • lymphatic TB (mass, possible overlying skin changes)

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Diagnosis

There are different diagnostic criteria and tests used for TB infection and TB disease.

Diagnosis of tuberculosis infection

The primary goal of testing for tuberculosis infection is to identify individuals who are at increased risk for developing TB disease in the future who would benefit from TB preventive treatment.

There are 2 accepted tests to identify TB infection:

  1. tuberculin skin test
  2. blood test (interferon gamma release assay)

Situations where one test is preferred over the other are outlined in the Canadian Tuberculosis Standards. Other tests and a clinical assessment are required for diagnosing TB disease.

TB diagnostic tests

Tuberculin skin test

A tuberculin skin test (TST), also called a Mantoux tuberculin test, is an antigen-based test for TB infection. The skin test is conducted by:

  • injecting a small amount of non-infectious purified protein derivative (made of TB antigens) intradermally under the surface of the patient's skin using a small needle
  • measuring the induration 2 or 3 days after the test

If the patient has been infected with TB previously, an induration (a hard, dense, and raised formation under the skin) will occur within 48 to 72 hours.

The area of induration should be objectively measured with a ruler. A measurement of less than 5 mm is generally considered negative. A measurement greater than 5 mm could be considered a positive result in some populations, whereas a threshold of 10 mm is used in others. For more details on the interpretation of TST results, including false positive and false negative results, please refer to the Canadian Tuberculosis Standards.

TB diagnostic tests

Blood test (interferon gamma release assay)

An interferon gamma release assay (IGRA) is a blood test that measures a person's immune response to MTB antigen to diagnose TB infection. IGRA is the preferred test when:

  • a person over the age of 2 has previously received the Bacille Calmette-Guérin vaccine (BCG) vaccine
  • a person is unable or unlikely to return to have their TST read
  • training and quality assessment are unavailable for TST administration or reading

The BCG vaccine is not recommended for universal use in Canada but is still used in some high incidence communities and high incidence countries. There are 2 assays currently approved for use in Canada:

  1. QuantiFERON-TB Gold In-Tube Plus assay (QFT-Plus)
  2. T-SPOT.TB (T-SPOT)

If blood test results are indeterminate, invalid, or borderline, the blood test should be repeated or a TST performed.

If a TST or IGRA is thought to be a true positive, then the possibility of TB disease should be ruled out prior to starting treatment for TB infection.

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Tuberculosis disease

Testing for TB disease is recommended:

  • in everyone considered to be at high risk of TB disease or with signs and symptoms of tuberculosis
  • when an individual tests positive for TB infection through a TST or blood test

The recommended steps for diagnosing TB disease are as follows.

  1. Do a complete medical history and examination.
  2. Order a chest X-ray.
  3. Order laboratory tests.

Every effort should be made to obtain a microbiological diagnosis.

In Canada, the standard testing algorithm for tuberculosis disease includes the following tests:

  • chest radiography (posterior-anterior and lateral)
    • chest radiography should be accompanied by microbiological tests for TB disease due to the low specificity of radiography alone
  • sputum smear microscopy
    • at least 3 sputum samples (either spontaneous or induced) should be collected and sent for smear microscopy to look for acid-fast bacilli (AFB)
    • sputum (phlegm) specimens should be collected a minimum of 1 hour apart
  • mycobacterial culture and phenotypic drug sensitivity testing (DST)
    • every specimen sent for smear microscopy should sent for bacterial culture
    • mycobacterial culture is the gold standards and is more sensitive than nucleic acid amplification testing (NAAT)
    • culture results typically take 2 to 8 weeks
    • rapid molecular tests for DST should be reserved for patients with a high pretest probability of multi-drug-resistant tuberculosis
  • nucleic acid amplification testing (NAAT)
    • NAAT can provide a rapid result and can be used to provide a rapid presumptive diagnosis of TB while awaiting culture results
    • NAAT should not be relied on to rule out TB disease
    • NAAT, particularly automated cartridge-based tests like GeneXprt, can be used in remote settings

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Prevention in health care settings

Exposure to people with undiagnosed pulmonary and laryngeal TB disease can occur in health care settings.

All health care settings should have a TB management or infection prevention and control program in place.

In a health care setting, infectious individuals should be placed in private (isolation) rooms. To contain the airborne pathogen and prevent the spread to other areas of the healthcare facility, isolation room must:

  • be at negative air pressure
  • have adequate ventilation, with the air directly exhausted to the outside or through a specially designed high-efficiency particulate air (HEPA) filtration system

Other additional precautions may be used, such as:

  • ultraviolet germicidal irradiation
  • HEPA filtration

When outside an airborne infection isolation room, masks should be worn by:

  • patients
  • people with suspected or confirmed pulmonary and laryngeal TB

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Treatment

TB infection treatment

Prior to starting treatment for TB infection, it is critical to rule out TB disease as this could result in undertreatment and possible drug resistance.

First-line therapy

First-line therapy can either be rifapentine and isoniazid for 3 months (3HP) once-weekly or rifampin for 4 months (4R) daily.

Further information on treatment details, alternative regimens and considerations for special populations can be found in the Canadian Tuberculosis Standards.

Tuberculosis preventive treatment in adults

Drug access for treating TB infection

Rifapentine (Priftin®) is not authorized for sale in Canada but is accessible for treatment of TB infection under an exceptional circumstances regulatory pathway, via a federal notification on drugs for urgent public health needs. This allows its importation from the United States into Canada for the treatment of TB infection in combination with isoniazid.

To order Priftin®and for additional information, please contact Sanofi (the manufacturer) at ADECPriftin@sanofi.com.

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TB disease treatment

The standard regimen for TB disease should include 2 effective drugs at all times, and at least 3 effective drugs in the intensive phase.

First-line therapy for suspected drug sensitive TB disease

Intensive phase (first 2 months):

  • isoniazid (INH)
  • rifampin (RMP)
  • pyrazinamide (PZA)
  • ethambutol (EMB)
    • can be stopped once confirmed to be drug sensitive through phenotypic or genotypic drug sensitivity testing

Continuation phase (following 4 months):

  • isoniazid (INH)
  • rifampin (RMP)

Treatment for drug-resistant TB is longer and requires a different combination of antimicrobial agents. Further information on treatment details and treatment of drug-resistance TB, including multi-drug resistant TB, can be found in the Canadian Tuberculosis Standards.

In addition, the standards can provide further guidance on the treatment of:

  • pediatric TB infection and TB disease
  • TB disease in people living with HIV (HIV co-infection)
  • extrapulmonary TB disease
  • TB disease in special populations

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Directly observed treatment

  • Can help to ensure that as close as possible to 100% of prescribed doses are taken.
  • Is a recommended approach for patients with risk factors for non-adherence.
  • Can be done in person, preferably in the community setting (rather than clinic setting) or consider new options such as video directly observed treatment.

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