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Tuberculosis

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Reporting Obligations

Clinical and or laboratory confirmed cases shall be reported to the local Health Unit. Positive tuberculin skin tests (LTBI) are also reportable.

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Epidemiology

Aetiologic Agent

The infectious agent is the Mycobacterium tuberculosis complex, which consists of Mycobacterium tuberculosis and includes M.canetti, M.africanum, M.caprae, M.microti, M.pinnipedii, and M.bovis. Mycobacteria are aerobic, non-spore forming and non-motile bacteria.

Clinical Presentation

Among those with newly developed latent TB infection (LTBI), approximately 90% will never develop active disease. The remaining 10% will develop active disease at some point in their lifetime, half of these within the first two years of infection. The risk of developing active TB is higher when other risk factors or comorbidities are involved, such as HIV co-infection. Those with HIV co-infection have an increased risk of 10% per year of developing active TB disease. Symptoms may include; persistent cough (of more than 3 weeks), sputum production (sometimes with hemoptysis), chest pain; and shortness of breath, fever and night sweats, loss of appetite and weight loss and fatigue.

Modes of Transmission

Transmission of tubercle bacilli in airborne droplets (1–5 microns in diameter) occurs with coughing, sneezing, singing or speaking. Several patient, pathogen and environmental factors determine whether transmission occurs. The droplets have an extremely slow settling rate which permits their transport by air currents, duct systems or elevator shafts for significant distances from the source case. Bacteria that are lodged on fomites (linen, furniture, books, floors) do not constitute a significant source of infection.

Transmission generally requires prolonged or repeated exposure to an infectious case. Laryngeal tuberculosis, although rare, is highly infectious. Healthcare workers may potentially be exposed during bronchoscopy, intubation and autopsy.

Incubation Period

Variable. 5% of infected individuals develop primary or progressive primary active disease within 18–24 months after infection, and 5% develop post primary disease over the remainder of their lifetime. While the subsequent risk of active pulmonary or extrapulmonary TB is greatest within the first 2 years after infection, without treatment, LTBI will persist for a lifetime. HIV co-infection and other immunocompromising conditions as well as age under 5 years increase the risk for the development of active TB disease following infection.

Period of Communicability

Communicable as long as viable tubercle bacilli are discharged in the sputum. The degree of communicability depends on the number of bacilli discharged, virulence of the bacilli, ventilation, and opportunities for aerosolization through coughing, sneezing, or during procedures such as intubation and bronchoscopy.

For smear positive or symptomatic infections the period of communicability may start up to 3 months before respiratory symptom onset; smear negative or asymptomatic cases with no evidence of cavities may be considered infectious up to 4 weeks prior to date of diagnosis.

For guidance on when to determine if a case is no longer infectious, or for details on when to discontinue airborne precautions, please refer to the Canadian Tuberculosis Standards (2014, or as current).

Children with primary pulmonary TB are generally not considered infectious.

Risk Factors/Susceptibility

The first 18–24 months after infection constitutes the most hazardous period for the development of clinical disease. Once infected, the risk of developing active TB disease is influenced by the time since infection, age, and medical conditions or therapies that affect the immune system of the infected person. The risk is highest in the persons recently infected (i.e., the first 1–2 years), very young children (under 5 years of age), and in persons who are immunosuppressed, particularly those who have HIV/AIDS, diabetes, and certain types of cancer.

Diagnosis and Laboratory Testing

The use of tuberculin skin test (TST) or interferon gamma release assay (IGRA) for the diagnosis of active TB in adults is not recommended. Testing for active tuberculosis (TB) is indicated for someone with signs and symptoms of TB or is considered to be at high risk of TB disease. Every effort should be made to obtain a microbiological diagnosis, which requires demonstration of acidfast bacilli on smear microscopy and/or culture of Mycobacterium tuberculosis. Chest radiography is an integral part of the TB diagnosis algorithm but cannot provide a conclusive diagnosis on its own. At least three sputum specimens should be collected and tested with microscopy as well as culture.

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Treatment and Case Management

Treatment is under the direction of the attending Health Care Provider. It is recommended that all active or suspect cases of TB be referred to a medical specialist knowledgeable and experienced in the clinical management of TB. Refer to the Canadian Tuberculosis Standards, 7th Edition, 2014. All close contacts will be notified by Public Health staff.

Publicly-funded rifapentine is only available to manage outbreaks and other exceptional circumstances. It has been included on Health Canada’s Access to Drugs in Exceptional Circumstances pathway and is not available through the Special Access Programme (SAP). See resource below.

Patient Information

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Additional Resources

Mantoux Tuberculin Skin Test Poster (administration of TST, reading results and interpretation)

Ontario Hospital Association. “Tuberculosis Surveillance Protocol for Ontario Hospitals.”

The Lung Association. “Tuberculosis Information for Health Care Providers, 5th Edition.”

Public Health Ontario. “Use of rifapentine and isoniazid combination therapy for the treatment of latent tuberculosis infection in Ontario, October 2018.”

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2019.

Public Health Agency of Canada, Canadian Tuberculosis Standards (7th Edition), 2014.