What IS TB?

TB is short for tuberculosis. TB is an infectious disease caused by a bactrium called Mycobaterium tuberculosis, or M.tb. These bacteria typically attack the lungs, but can cause disease in multiple organ. Not everyone infected with M.tb will become sick with TB disease. Infection, as opposed to active disease, is commonly referred to as latent tuberculosis infection (LTBI). Both TB disease and LTBI can be treated. Treatment reduces individual morbidity (sickness) and mortality (death), potential infection-spreading cases, and public health impacts. Treatment of LTBI reduces the individual risk of developing disease in the future.

How Does TB Spread?

Not all forms of TB are infectious. TB can infect many organs but only TB in the lungs is infectious. TB is transmitted by aerosols in the air. Infectious plumes are generated by people with active TB disease in their lungs (pulmonary TB). Aerosolization is caused by coughing or sneezing, whereby infection-laden particles are generated. These particles stay suspended in the air, where they can be inhaled by people breathing nearby. A single inhaled bacterium can establish a new infection.

Mycobacterium tuberculosis


M.tb resembles many bacteria, but it has unique features that makes it difficult to diagnose and treat.

Unique Cell Wall

The M.tb cell wall is thick, with a waxy coating primarily composed of mycolic acids. This coating allows the bacteria to lie dormant for many years

Slow Growing

M.tb slow growing bacteria that reproduces every 24-48 hours which is very slow for a bacteria.

Life Span

M.tb can survive outside the body for up to six months if they are protected from direct sunlight.

Active and Latent tuberculosis

Exposure to the TB bacteria does not always lead to an infection or disease. It is estimated that only about 30% of those exposed become infected.

Most people who are infected by M.tb maintain a latent TB infection (LTBI) and persist undetected for many years. LTBI is not associated with symptoms, and it is not an infectious state. LTBI can, however, progress into an active form of disease if the body’s immune defenses are compromised (weakened). This progression is known as reactivation and occurs in about 5-15% of people with LTBI, and typically within the first 2-5 years following infection. These realities highlight the importance of treating both active TB disease and LTBI wherever possible to achieve elimination.

A Global Perspective

One quarter to one third of the world’s population is infected with TB. This constitutes an enormous reservoir of potential disease. This is why detecting and treating individuals with LTBI is very important. In fact, the risk of reactivation can be greatly reduced with preventive therapy.

Latent TB in Canada

TB reactivation from untreated LTBI is a major source of new active TB infections and transmission. It accounts for the majority of new TB cases in countries like Canada, where overall TB incidence is low.

Targeted LTBI screening, testing, and treatment of marginalized and hard-to-access groups and those with high risk for TB reactivation, is a priority (click here to learn more about TB in Canada and populations most at risk).

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Learn more at:

Canadian Communicable Disease Report: Latent TB Infection Overview

The WHO End TB Strategy

The Canadian Federal framework for Action on TB Prevention and Control

LTBI diagnosis:  https://www.tbinfocus.ca/tb-diagnosis/

LTBI treatment: https://www.tbinfocus.ca/tb-treatment/


Multi-Drug Resistant tuberculosis

Antimicrobial resistance occurs naturally over time through genetic changes. However, the misuse and overuse of antimicrobial drugs are accelerating this process. Drug-resistant TB develops when the long, complex, decades-old TB drug regimen is improperly administered, or when people with TB stop taking their medicines before the disease has been fully eradicated from their body. Multi drug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) are difficult to cure, and even when long, burdensome treatment regimens are completed. Both MDR-TB and XDR-TB have high mortality rates. MDR-TB and XDR-TB are spread just like susceptible TB.

Multi-drug resistant Tuberculosis (MDR-TB)

Multi drug-resistant tuberculosis (MDR-TB), defined as TB resistant to both isoniazid (INH) and rifampin (RIF), both first-line drugs used in the standard TB treatment regimens.

Extensively drug-resistant tuberculosis (XDR-TB)

Extensively drug-resistant tuberculosis (XDR-TB), defined as resistance to INH, RIF, fluoroquinolones and one or more injectable drugs (amikacin, kanamycin, or capreomycin).

Global MDR- TB

About 29% of deaths caused by microbial infections today are due to drug-resistant TB. Globally in 2013, it is estimated that 480,000 people developed drug-resistant TB. People with drug-resistant TB must resort to second-line drugs, which are more toxic, less effective, take longer to treat the disease, and are more expensive.

Research Findings

Multidrug and Extensively Drug-Resistant TB in Canada 1997-2008: Demographic and Disease Characteristics (2013)
Minion J, Gallant V, Wolfe J, Jamieson F, Long R.

Increase in Multidrug-resistant Tuberculosis (MDR-TB) in Alberta Among Foreign-born Persons: Implications for Tuberculosis Management(2013)
Richard Long, MD & Deanne Langlois-Klassen, PhD

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