Tuberculosis: For health professionals

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What health professionals need to know about tuberculosis

Tuberculosis is an infectious disease caused by the bacteria Mycobacterium tuberculosis.

Of the people who are infected:

  • about 5% will develop active tuberculosis disease within 18 to 24 months
  • about 95% will develop latent tuberculosis infection, of which:
    • about 90% will never develop active tuberculosis disease
    • 5% will have a reactivation and develop active tuberculosis at any point after initial infection

Tuberculosis usually affects the lungs, but may also affect other organs, such as the:

  • brain
  • spine
  • bones
  • kidneys
  • lymph nodes

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

Diagnosis

There are 2 types of tuberculosis infection:

  1. latent tuberculosis infection
  2. active tuberculosis disease

Latent tuberculosis infection (LTBI)

There are 2 accepted tests for identification of latent tuberculosis infection:

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

Preference and exceptions are outlined in the Canadian Tuberculosis Standards.

Tuberculosis skin test

A tuberculin skin test (also called a Mantoux tuberculin test) is used to see if you have been exposed to tuberculosis and perhaps have latent tuberculosis infection or active tuberculosis disease. The skin test is conducted by:

  • injecting a small amount of non-infectious tuberculosis protein under the surface of the patient's skin using a small needle
  • measuring the patient's reaction 2 or 3 days after the test

If the patient is infected with tuberculosis, a skin reaction will occur within 48 to 72 hours. The spot where the needle was injected will develop an area of redness with possible hardening (induration).

The area of hardness (not redness) should be objectively measured with a ruler. A measurement of more than 5 mm could be considered a positive result.

Inform your patient if the test is positive or negative.

A positive skin test

If a patient has a positive test result, you may need to:

  • investigate further to rule out a false positive
  • do more tests to find out if the patient has active tuberculosis disease

You may also need to:

  • assess signs and symptoms suggestive of possible active tuberculosis disease
  • assess patient risk factors
  • order a chest X-ray

In the presence of symptoms or abnormal chest X-ray, sputum for acid-fast bacteria smear and culture should be taken.

A positive test can happen even if a patient does not have a latent tuberculosis infection. This can happen in people who have been:

A negative skin test

A negative test result can happen even if a patient has tuberculosis bacteria in their body. This can occur if they have:

  • a weak immune system due to:
    • an HIV infection
    • active tuberculosis disease
  • recently been infected by a person with active tuberculosis disease:
    • it takes 3 to 8 weeks after exposure for the skin test to become positive

Blood test (interferon gamma release assay)

A blood test for latent tuberculosis infection is:

  • not recommended for routine diagnosis of latent tuberculosis infection
  • only used under special circumstances

Active tuberculosis disease

Testing for active tuberculosis is indicated:

There are 3 steps in diagnosing active tuberculosis disease:

  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 active tuberculosis includes the following tests:

  • chest radiography
    • chest radiography cannot provide a conclusive diagnosis on its own
    • it should be followed by microbiological tests for tuberculosis
  • sputum smear microscopy
    • everyone with suspected tuberculosis should undergo testing with at least 3 concentrated fluorescent smears
    • sputum (phlegm) specimens should be collected a minimum of 1 hour apart
    • same-day collection may be considered to reduce patient drop-out
  • mycobacterial culture and phenotypic drug sensitivity testing (DST)
    • every specimen sent for smear microscopy should be set up for culture in 1 solid and 1 liquid medium
    • culture results typically take 2 to 8 weeks
    • phenotypic DST should be routinely performed for all first positive culture isolates obtained from each new tuberculosis case
    • 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)
    • take at least 1 respiratory sample with Health Canada-approved or -validated in-house NAAT in all new, smear-positive cases
    • NAAT may also be performed in smear-negative patients

Prevention in health care settings

The incidence of active tuberculosis in Canada is generally low. However, exposure to people with undiagnosed active respiratory tuberculosis disease does occur in health care settings.

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

In a health care setting, infectious individuals should be placed in private (isolation) rooms.

To dilute the concentration of contaminants in an isolation room, the room must:

  • have adequate ventilation
  • be at negative air pressure

The air from the isolation room must be directly exhausted to the outside.

Other additional precautions may be used, such as:

  • ultraviolet germicidal irradiation
  • high-efficiency particulate air (HEPA) filtration

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

  • patients
  • people with suspected or confirmed respiratory tuberculosis

Treatment

Antibiotic drugs can cure active tuberculosis disease. All patients with active tuberculosis in Canada should be treated initially with a regimen of:

  • isoniazid (INH)
  • rifampin (RMP)
  • pyrazinamide (PZA)
  • ethambutol (EMB)

If the isolate causing disease is fully susceptible to all first-line drugs:

  • EMB can be stopped
  • PZA should be given for the first 2 months
  • after that, only INH and RMP are required for the remainder of therapy, usually for another 4 months

The Canadian Tuberculosis Standards can provide further guidance on the treatment of:

  • latent tuberculosis infection
  • pediatric tuberculosis
  • drug-resistant tuberculosis
  • HIV-associated tuberculosis
  • extrapulmonary tuberculosis

Directly observed treatment:

  • can ensure that 100% of prescribed doses are taken
  • is a recommended approach for patients with risk factors for non-adherence

The standard regimen of first choice for treating latent tuberculosis infection is 9 months of daily self-administered INH. More information is provided in the Canadian Tuberculosis Standards.

In some cases, patients with latent tuberculosis infection should be treated following the World Health Organization’s recommended treatment:

  • 6-month or 9-month INH weekly
  • 3-month rifapentine plus INH weekly
  • 3- or 4-month INH plus RMP daily
  • 3- or 4-month RMP alone daily

More information is provided in the Canadian Tuberculosis Standards.

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