Tuberculosis: Are you at risk?

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Quebec’s public health department has announced that it’s looking for passengers who were on either of two Megabus routes between Toronto and Montreal in August, because they may have been exposed to tuberculosis.

Many people are now asking what tuberculosis is, what risks the passengers face, and whether the general public should be concerned. So here is a brief review.

Tuberculosis, which is known as TB, is one of the most common bacterial infections on the planet, affecting two billion people worldwide.

READ MORE: Toronto-Montreal Megabus passengers potentially exposed to TB, health officials warn

Although 95 per cent of these cases are in developing countries — even in Canada, in our First Nations populations, and in cities with large immigrant populations such as Toronto, TB is not uncommon.

The infection can affect any part of the body, but as a lung specialist, I often see TB because it’s a disease that enters the body through the lungs and primarily affects the lungs.

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When a person with active infection coughs, tiny droplets of liquid carrying the TB bacteria are released into the air.

These droplets can stay in the air for several hours, and if someone else happens to breathe one in, the bacteria travel through the airways and end up deep in the lungs.

What’s interesting about TB is that most people don’t get an immediate infection. In the majority of people, the body either kills the bacteria completely, or is able to contain the infection by forming a scar around the bacteria.

This is called latent TB, and people who have this are completely well with no symptoms.

The problem is that in five to 10 per cent of these people, usually years later, those bacteria reactivate and start to grow — causing an active infection.

Once the infection is active, the person will develop cough, phlegm, and often fever and weight loss.

The problem is that the infection might initially feel like a bronchitis or a conventional pneumonia, and people often don’t realize they have TB until they get really sick, by which time they’ve had symptoms for several days and often have exposed several others.

And this is a particular concern in tight spaces where people are sharing the same air for a long period, such as airplanes and buses.

So it’s likely that the person who took this bus trip didn’t know that they had TB, and if they were coughing, they may have spread it to others on the bus.

The people at highest risk would be those who sat close to this person and/or who spoke to them directly.

Although it’s rare, I have seen a few cases of TB in patients who are born and raised in Canada and were exposed to somebody with TB right here at home without even knowing it.

The key is to now trace everyone who might have been exposed so that we can minimize the chances of further infections and further spread.

The good news is that for anyone who was exposed, we have a simple skin test or blood test which we use to diagnose latent TB, and we have antibiotics that can kill off the bacteria to prevent a full blown infection.