TB or Not TB?

Today in morning report we talked about Tuberculosis (TB). TB has a major global disease burden, the WHO estimates that 1/3 of the worlds population is infected with Mycobacterium tuberculosis. Although Canada has a low incidence of TB overall, a substantial proportion of patients with active TB in Canada are diagnosed in the Greater Toronto Area (around 30% of Canadian cases, 75% of cases in Ontario). This is likely driven by high immigration rates from endemic countries (less than 1% of cases are in the aboriginal population). TB is usually managed in the ambulatory setting, however requires close case management and follow up, and coordination of multiple diagnostic and consultation services.

tb-distribution-canada.png
Via 7th Edition Canadian Tuberculosis Standards

The terminology with TB is important to understand to put our current treatment and screening strategy in context. Understanding the terminology, starts with the natural history of TB. Most people who are infected with TB will not have disease at the time they are infected and will progress to latent TB infection (95%). Children under 5 and patients with immunocompromising conditions such as HIV have a higher rate of developing primary disease.

Latent TB re-activates in about 5% of patients. High risk factors for re-activation include: immunocompromised (either through medication or HIV), chronic kidney disease on dialysis, silicosis, or carcinoma of the head and neck. Patient on glucocorticoids, TNF alpha inhibitors, or those with diabetes, poor nutritional status, smoking and heavy alcohol consumption are moderate risk of disease recurrence.  Despite this, most cases in Ontario do not have an identifiable risk factor for TB re-activation. The main risk factor for TB in Ontario is that you were born or have resided in a country with higher disease prevalence.  However, all patients with confirmed TB should have HIV testing due to implications for disease activity and treatment.

TB pathogenesis
Pathogenesis of Tuberculosis in the infected host. From 7th Edition Canadian Tuberculosis Standards.

So practically speaking, when should you suspect someone has active TB?

Clinically, the symptoms of Respiratory TB re-activation are:

  • “Classic” symptoms of TB: cough x 2 weeks, fever, night sweats.
  • Associated symptoms of TB: Hemoptysis, anorexia, weight loss, chest pain

Respiratory TB:

  • Pulmonary TB: disease limited to the lung paryenchema
    • Lungs
    • Conducting airways
    • TB pneumonia
    • TB Fibrosis
  • Non-pulmonary TB:
    • Pleural disease (TB Pleurisy, TB Empyema)
    • Lymphatic Disease – lymphadenopathy of intrathoracic and mediastinal lymph nodes
    • Nasopharynx/Nose/Sinuses
441px-Extrapulmonary_tuberculosis_symptoms.svg
Via Wikimedia commons

Non-respiratory TB (also non-pulmonary TB):

  • Lymphatic Disease – lymphadenopathy (outside of the mediastinum, thorax)
  • Meningitis – headache, neck stiffness
  • Miliary TB – Hematogenous spread
  • Osteomyelitis – bone pain, swelling
  • Pott’s Disease – chronic back pain, spinal compression, abscess
  • Genitourinary – infertility, renal TB (recurrent sterile pyelonephritis)

How to Diagnose Active TB:

If you suspect someone has TB and they are producing sputum you can send a sample for an AFB smear. However, a single negative AFB smear does not rule out the diagnosis of TB.  Three sputum specimens should be collected at a minimum of 1 hour apart. They must be transported to the laboraroy within 1 hour or stored in a refrigerator if there will be a delay. Patients should be instructed not to rinse their mouths with tap water as it may contain environmental mycobacteria (NTM).

Induced sputum samples have a sensitivity of 75% and can be helpful to confirm a diagnosis if a patient is not producing sputum. Like with spontaneous sputum, 3 samples collected at least 1 hour apart are required.

If the spontaneous sputum samples or induced sputum are negative, or if they do not produce a high quality sample, and the clinical suspicion is still high, the patient should be referred for bronchoscopy.

If non-respiratory TB is suspected, biopsy and culture of the affected area should be pursued. It is important to check the most up to date guidelines at your site for TB culture and specimen handling instructions as the lab will often require higher volume of specimen to process the sample (e.g. over 2mL of CSF).

Once a diagnosis is confirmed, all cases of active tuberculosis should be treated by a clinician with TB experience. All patients should be managed with airborne precautions and/or home isolation until no longer infectious, in consultation with your local public health unit. Patients with non-respiratory TB should also be managed with airborne precautions until respiratory TB is ruled out.

If TB still confuses you, that’s okay it confuses me too! There are great resources through the lung association and guidelines through Public Health Canada that are worthwhile to refer to when you suspect a case.

Some take away points:

  • There is a huge global burden of TB infection, in Canada most cases are diagnosed in the greater Toronto area in people who were born or have lived in endemic regions of Asia and Africa.
  • Have a low threshold to suspect TB in a patient with possible TB symptoms chronic cough, weight loss, hemoptysis, particularly if they have immigrated from an enedemic area.
  • Testing requires at least three spontaneous or induced sputum samples collected at least 1 hour apart
  • Test all new cases of TB for HIV (especially cases of non-pulmonary TB)
  • TB care is collaborative, it may require respiratory technologists, TB infectious disease specialists, respirologists, thoracic surgeons or general surgeons to confirm the diagnosis and initiate treatment.

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