Every four seconds someone in the world is infected with Mycobacterium tuberculosis, the main organism causing tuberculosis (TB), an infection characterized by persistent cough, fever, weight loss and night sweats. More disturbingly, someone in the world dies of TB every 19 seconds. Here's what you need to know about TB.

1. Most cases of TB in Canada originate outside the country
Aboriginals, the homeless and drug users help to make up one-third of TB cases in Canada. The remaining cases are among people who were infected while living in or visiting areas of the world where TB is rampant.

Infection typically occurs when someone with active disease (of the lungs or airways) coughs or sneezes. Following infection, the bacteria are likely to remain walled off in the lungs, where the body keeps the infection at bay -- sometimes for decades -- until age, HIV infection or treatment with drugs that depress the immune system might cause it to break out, says Dr. Edward Ellis, the manager of tuberculosis prevention and control for the Public Health Agency of Canada in Ottawa.

Although TB bacteria mostly attack the lungs, they can also affect bones, joints, lymph nodes and kidneys. The general risk of developing active TB following infection is approximately 10 per cent over a lifetime, but that risk is largely concentrated in the first two years, when there's a five per cent chance of developing active disease.

2. Even those with dormant TB infection should be treated
People with active TB (as detected on chest X-ray and skin test) must follow an antibiotic regimen that consists of a minimum of three antibiotics for at least six months. Too often people stop taking their medicine because they're feeling fine. “People start gaining weight, they're sleeping fine without sweating -- and [then] the bacteria come back,&" says Ellis. Not completing the antibiotic course can result in bacteria becoming drug resistant.

People with dormant or latent TB should take an antibiotic, too (experts recommend izoniazid) to prevent the infection from progressing to active TB. “People with latent TB are not infectious to others and they feel fine,&" says Ellis, but if someone tests positive for TB, “why run the risk of having TB in the future when you can take a pill now and virtually eliminate that risk.&" Taken faithfully, anti-TB drugs can cure more than 90 per cent of infections.

3. Everyone who comes into close contact with an infected person needs to be notified and tested for TB
Physicians are required to report a person with TB to public health officials, who then attempt to track down that person's recent contacts. For example, if a person diagnosed with TB has been coughing for a month, “we will go back at least one month and assess people he or she has been most in contact with, typically household members and close personal friends,&" says Ellis.

All contacts undergo a chest X-ray and skin test. Anyone who tests positive -- the likelihood depends on how much the index person coughed or sneezed, how much bacteria was in the airborne sputum and how robust the contact individual's immune system was at the time of contact -- will be offered the six-month preventive antibiotic regimen.

4. TB in Canada is rarely fatal
In 2005, officials recorded 1,616 new cases of active TB in Canada, and in 2004, there were only 27 deaths from TB. However, the disease is not insignificant: people still get sick with TB, and the disruption they face at work and home can be serious, says Ellis. It also takes six months to treat, and six months on antibiotic therapy is arguably not trivial either, he says.

TB and vaccination
No vaccine is available yet to prevent infection with tuberculosis (TB), but there is a vaccine that can limit the spread of the bacteria in young children following infection, and it's being used in areas where the risk of TB infection is high.

If you're travelling to a developing country where there is still a lot of TB, “speak to your doctor about getting the TB skin test when you return,&" advises Dr. Edward Eillis, the manager of tuberculosis control for the Public Health Agency of Canada in Ottawa.

If positive, you should seriously consider taking the antibiotic izoniazid. “If you take it faithfully for at least six months,&" says Ellis, “it will dramatically reduce your chances of developing TB disease in the future.&"

From the World Health Organization

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