Epidemiology of TB
Middlesex-London has an average of 10 active TB cases per year. Nationally, TB prevalence is estimated to be 5.6 per 100,000. See the World Health Organization (WHO) website to view Canada's TB profile. Many other countries around the world have prevalence rates much higher than Canada. To find the TB prevalence in other countries, click here to view the online WHO resource that allows you to directly type in your patient’s country of origin.
Diagnosing inactive (latent) TB
When an individual has frequent and prolonged exposure to a person with infectious active TB, they may develop inactive TB. TB skin tests (TSTs) have been used for a long time to help health care providers assess a person’s exposure to TB.
It is important to understand that TSTs are NOT used to diagnose active TB disease, rather a positive TST helps diagnose inactive TB.
The TST is frequently used to screen target populations for evidence of inactive TB. These screening programs often employ the 2-step TST method. The advantage of the 2-step method is it provides a baseline reading. Once a person has received a negative 2-step TST ALL future screening requires only a single TST.
Any person found to have a positive TST requires a medical exam, chest radiograph and sputum testing if symptomatic. This will help rule out active TB disease (particularly if person identifies any symptoms such as fever, cough, night sweats or weight loss). The x-ray may also help further confirm the inactive TB diagnosis (i.e. calcified granulomas) and rule out active TB.
Inactive TB treatment
Healthy persons with a positive TST and a normal chest x-ray have a 10% lifetime risk of progressing to active TB (5% within 2 years of infection and 5% the rest of their lifetime). Treatment of inactive TB can reduce that lifetime risk of developing active disease to approximately 1%. The decision to treat inactive TB is dependent on underlying risk factors that may increase the risk of developing active disease, the age of the client, the presence of medical contraindications, and the risk of drug induced hepatitis. The standard treatment for adults with inactive TB is Isoniazid (PDF 74KB) 300mg daily for 9 months. Children should be treated with a dose of 10 to 15 mg/kg per day up to a dose of 300 mg, for 9 months. For more information on treating inactive TB see Quick Reference - Assessment and treatment of latent Tuberculosis Infection. Remember that active TB must be ruled out before beginning treatment of inactive TB.
The Online TST/IGRA Interpreter is an excellent interactive tool that provides an estimate of a person’s lifetime risk for developing active TB and potential risk for drug-induced hepatitis.
All medication for the treatment of inactive TB can be ordered free-of-charge from the Middlesex-London Health Unit by faxing a TB Medication Prescription and Order Form to: 519-663-8241. A Public Health Nurse will collect required information (demographic, TST/IGRA results & recent chest x-ray result) and package up a 3 month supply of medication for pick-up. Please note, the health unit will not dispense directly to clients.
TST’s and IGRA
While TSTs have been used for decades in the identification and management of inactive TB, newer blood tests called Interferon Gamma Release Assays (IGRAs) are becoming more widely available. While the sensitivity and specificity of IGRAs may be comparable to the traditional TST, the IGRA is currently not covered by OHIP. Contact Gamma-Dynacare Medical Laboratories London Ontario 245 Pall Mall Street at (519) 679-1630 for testing details.
Diagnosing Active TB
The gold standard for diagnosing active pulmonary TB is “sputum collection”. A clinical diagnosis of active TB is possible, but every effort should be made to obtain laboratory confirmation in all cases. Laboratory confirmation is important in assessing infectiousness and the possibility of antibiotic resistant strains of TB. A sputum sample before beginning therapy will help guide duration of isolation (AFB results) and medication selection (sensitivities). The Health Unit can assist in specimen collection if there is a suspicion of TB.
For more information about sputum collection for patients, download the Middlesex-London Health Unit's Sputum Collection Fact Sheet (PDF 67KB).
Active TB medications
The objectives of treatment and management of active TB disease are to achieve a life time cure while preventing drug resistance and limiting transmission. In general, all cases of active TB should be managed by an infectious disease specialist or respirologist and public health can assist with any necessary referrals. Cases of active pulmonary TB receive at least 8 weeks of direct observed therapy (DOT) by a Public Health Nurse to assess medication compliance.
All medication for the treatment of TB can be ordered free-of-charge from the Middlesex-London Health Unit by calling (519) 663-5317 ext. 2330.
Please refer to the Canadian TB Standards 7th edition for treament information.
Non-Tuberculosis mycobacterium (NTM)
TB belongs to a family of bacteria known as mycobacterium. Frequently, an investigation of suspected TB reveals one of the other mycobacterium (not TB). Non-tuberculosis mycobacterium (NTM) infections are NOT reportable to Public Health once active TB has been ruled out. The Canadian TB Standards 7th edition provides more information on NTMs.
Bacille Calmette-Guérin (BCG)
For over 100 years, BCG vaccination has been used to aid in TB control in many countries. However, the efficacy of BCG vaccine remains controversial. Although the National Advisory Committee on Immunization (NACI) does not recommend BCG vaccination as part of the Canadian TB Control strategy, over 100 countries still utilize the vaccine (especially in the less than 1 year of age population). Therefore, many people who have immigrated to Canada may have had BCG.
BCG vaccination can cause “false positive” TST results. However, a history of BCG vaccination should not influence the decision to treat latent TB infection, especially if the person being tested received BCG under 1 year of age and is now 10 years of age or older. In this case, the positive TB skin test is unlikely to be from the BCG vaccine.
IGRA testing may be considered for individuals with positive TSTs who also have a history of BCG vaccine. This may help rule out a “false positive” TST result. Contact Gamma-Dynacare Medical Laboratories - London Ontario - 245 Pall Mall Street at (519) 679-1630 for testing details.
The BCG World Atlas is an online tool which allows health care providers to search over 180 countries practices governing BCG use.
TB and HIV co-infection
All suspected or confirmed cases of TB should be screened for HIV. Conversely, all HIV cases should be tested for TB. The Candian TB Standards has more information about TB and HIV co-infection.