News

The global impact of tuberculosis is staggering. An estimated one in three humans is infected with the bacilli; 5-10 per cent will become sick and contagious.

The World Health Organization estimates 1.5-million people died as a result of the disease in 2006. That same year, there were 1,620 cases of new active and relapsed TB in Canada. At least 70 Canadians died of TB-related causes in 2004, according to the most recent numbers from Statistics Canada.

Canadians might be surprised to learn the prevalence of the disease in this country. Perhaps as surprising is the number of federal investigations launched each year into cases of infectious TB with a history of air travel into and out of Canada.

As The Globe's Brodie Fenlon reported Monday , Canadian health officials have tracked down hundreds of passengers on long-haul flights in recent years who may have sat near an infected patient. In some cases, they weren't able to identify these "contacts" because the airlines failed to provide them with passenger manifests.

What is tuberculosis? How dangerous is it? How is it spread? How is it treated?

We are pleased to welcome one of Canada's foremost TB experts online to take your questions about the disease.

Dr. Michael Gardam will join us Monday at 3:30 p.m. ET. Send us your questions now through our comment function.

Dr. Gardam is the director of Infectious Diseases Prevention and Control for the Ontario Agency for Health Protection and Promotion. He is also the medical director of the tuberculosis clinic at Toronto Western Hospital and director of the Infection Prevention and Control Unit at the University Health Network.

Dr. Gardam completed his undergraduate degree, master's degree, and medical school training at McGill University in Montreal. He completed training in internal medicine and infectious diseases and became a Fellow of the Royal College of Physicians and Surgeons of Canada in infectious diseases in 1998.

Dr. Gardam finished a second master's degree in health policy, management and evaluation at the University of Toronto in 2003. He is an assistant professor of medicine at the Dalla Lana School of Public Health at the University of Toronto and secretary of the Association of Medical Microbiology and Infectious Disease Canada, as well as a member of the Community and Hospital Infection Control Association Canada.

Dr. Gardam has acted as a consultant on infection control issues such as SARS, tuberculosis, pandemic influenza and C. difficile, at the provincial, national and international level. Within Ontario, he has helped a number of hospitals control outbreaks and develop their infection control programs.

Editor's Note: globeandmail.com editors read and allow or reject each question/comment. Comments/questions may be edited for length or clarity. HTML is not allowed. We will not publish questions/comments that include personal attacks on participants in these discussions, that make false or unsubstantiated allegations, that purport to quote people or reports where the purported quote or fact cannot be easily verified, or questions/comments that include vulgar language or libellous statements. Preference will be given to readers who submit questions/comments using their full name and home town, rather than a pseudonym.

Brodie Fenlon, globeandmail.com: Thanks for joining us Dr. Gardam. When I interviewed you last week, you said that it is usually pretty hard to catch TB, and that's one message that is sometimes hard to get across because the public is used to the concept of influenza and SARS. I wonder if you could elaborate on this? I think some people think catching TB is as easy as catching a cold.

Dr. Michael Gardam: TB is probably the only infectious disease that spreads entirely through the airborne route -- meaning that you have to breathe it into your lungs to get infected. When somebody with TB coughs into a room, tiny infectious particles end up floating on the air currents. If the ventilation in the room is good, these particles will be whisked away and diluted out.

This is different from other infections like cold and flu or SARS viruses that likely transmit through several ways, including through contact with your nose and throat, either directly or through your hands. In general, it takes prolonged exposure to contaminated air, i.e. hours to days, to become infected with TB. Rarely however, infection can occur quickly if the setting is right: a highly infectious patient coughing into a small room where there is poor or no ventilation.

Backseat Driver from Guelph writes: Is a TB skin test really necessary for new employees who are hired to work at an Ontario health unit? Isn't it overkill - especially when you know the person is not a recent arrival from a country where TB is endemic.

Dr. Michael Gardam: The main reason we skin test health-care workers (and I would include people who work in a health unit in that broad category) is because we want a baseline result to be able to compare with should they ever become exposed to TB. Depending what one's role is in a health unit, this could be a real possibility. If we know that you are negative on hire but then become positive after an exposure, it is pretty easy to figure out that you became infected. Similarly, if you are positive on hire, we know that testing you post-exposure will not be helpful (once the test is positive, it is no longer useful to keep retesting people).

Another lesser reason to test people in health care is to ensure they do not have active tuberculosis prior to starting work -- you can imagine that this almost never occurs and skin testing isn't a great way of diagnosing active TB anyway. The main reason to test is to get a baseline.

Pants 7 from Japan writes: What would be the advantages and disadvantages of a national BCG vaccination program or a BCG vaccination program on reserves?

Dr. Michael Gardam: I am going to do this question a disservice by providing a short answer, because a complete answer will take too much time! In short, the BCG vaccine (which is not given in Canada, with a few exceptions in some First Nations communities) seems to protect young children from dying from TB and from having TB meningitis (a rare but very deadly form of the disease). It does not seem to protect children from lung TB and overall doesn't seem to have a significant protective effect in adults.

If you vaccinate children at age less than one year, their skin test may be falsely postive for several years thereafter. If you vaccinate them in older years, the vaccine may cause positive skin tests many years later.

So, if you decide to vaccinate a community, you cannot rely on skin testing to determine if young children have been infected with TB.

BCG vaccination would be recommended in populations where there is enough TB around that you are seeing a significant number of cases in young children meaning that there is active transmission of TB ongoing. BCG will at least partially protect them. Once the rate of TB goes down though, we normally stop vaccinating and shift to a skin testing policy.

Finally, the BCG is not entirely benign in that it is a live vaccine -- rarely, children who have immunodefficiency diseases can develop serious infections from BCG. As the rate of TB goes down in a population, the risk of BCG vaccination starts to outweigh the potential benefits.

Brodie Fenlon, globeandmail.com: Could you tell us more about the Canadian situation? Are there populations more likely to get active TB? How successful are we at treatment?

Dr. Michael Gardam: There are several populations at risk for becoming infected with TB. These include: foreign-born individuals coming from countries where there is still lots of TB; health-care workers; people who travel to high-risk countries; homeless populations; prison inmates and prison staff; and some First Nations communities.

Once infected, a healthy person has a 5-10 per cent chance over their lifetime of developing active TB. Most of this risk is in the first few years after becoming infected. People are more likely to get active TB if they have underlying medical illnesses--the most blatant example is AIDS where the risk is 170-fold higher than in someone who is healthy.

In terms of treatment, there are two general strategies: people who are infected, i.e. have a positive tuberculin skin test but have no symptoms (called "latent infection"), can be offered "preventative therapy." They're given a TB antibiotic that kills off the dormant organisms inside the body. This can decrease your risk of getting active TB up to 90 per cent. To be clear, people with latent infection are not sick and are not contagious; they just run the risk of developing active disease at some point.

People with active tuberculosis (defined as having symptoms and evidence of an ongoing active infection) are treated with a combination of TB antibiotics for at least 6 months. The cure rate is greater than 97 per cent if the bacteria is sensitive to the antibiotics.

People with active tuberculosis (defined as having symptoms and evidence of an ongoing active infection) are treated with a combination of TB antibiotics for at least 6 months. The cure rate is greater than 97 per cent if the bacteria is sensitive to the antibiotics.

Derek Congram from Vancouver writes: I'm a bioarchaeologist (archaeologist specializing in the analysis of the human skeleton) at Simon Fraser University. I'm currently examining a skeleton with fairly dramatic lesions on the pelvis that appear to be the result of TB. My question is: is that person likely to have known that they were infected during life and if so, is that person likely to have sought treatment (assuming that they died recently)?

Dr. Michael Gardam: Usually bone TB is quite painful so I would assume the person knew they had something going on. They wouldn't necessarily know it was TB unless the lesions were biopsied and/or cultured for TB. If TB was a real possibility, they presumably would have been offered treatment. The treatment for bone TB is essentially the same as for lung TB except that we often tend to treat a bit longer (9-12 months).

On the discussion page to the story, Scrappy T from Canada writes: What happened to the time when you had to prove, with a document, that you had received all the inoculations required before you could board a plane? This was at a time when there wasn't as much international travel.

Dr. Michael Gardam: Those days are long gone! In terms of TB, it wouldn't be helpful anyway as the BCG is really only protective for young children (the efficacy of the BCG vaccine is highly controversial and no doubt you will find people who disagree with what I just wrote).

Brodie Fenlon, globeandmail.com: I'd like to know about multidrug-resistant and extensive drug-resistant TB. How serious is it? Do we have these strains in Canada? What are you treatment options and how successful are they?

Dr. Michael Gardam: MDR and XDR TB strains are extremely serious. MDR TB is defined as TB that is resistant to the two best drugs we have to treat it. Instead of curing 97 per cent of patients in 6 months, the MDR TB cure rate is closer to 70 per cent and we have to treat for upwards of two years. Also, the drugs we have to use tend to be more toxic and less effective.

XDR TB is MDR TB that is resistant to several more classes of antibiotics. The cure rate for this form of TB is abysmal and treatment will typically involve using surgical techniques that have not been used in decades -- namely trying to cut out infected parts of the body wherever possible. For XDR TB cures, we go back to the time of the TB sanatoria before we had effective medications (for an in-depth and personal look at this era of treatment, I suggest reading "The Magic Mountain" by Thomas Mann).

Both MDR and XDR TB are increasing in the world. It is just a matter of time before we see more cases in Canada.

Roman Spears from St. Catharines, Canada writes: Many years back, after several negative skin tests, I had a positive reaction. I was given a multitude of X-rays and other tests, including a bronchoscopy. It showed I did not have TB. It was interpreted as my likely having been exposed to the disease at some point in time. Does this mean I am (or could be) immune to TB or just a variant of TB, or not immune at all?

Dr. Michael Gardam: When someone goes from having a negative tuberculin skin test to a positive, it is typically interpreted that you have become infected with TB bacteria. Being infected while having no symptoms is called "latent infection." In this circumstance, the TB bacteria is alive inside of you but it is not doing anthing -- your immune system has walled it off and the bacteria is a latent state. People with latent infection have a 5 to 10 per cent chance of developing active TB (i.e., the TB starts to grow and you start having symptoms) over their lifetime, with most of the risk occurring in the first two years after you became infected.

So in your case, it appears you converted your skin test from negative to positive and then were appropriately investigated for active TB. This investigation usually involves having a chest X-ray and a physical exam and possibly collecting a sputum sample such as you did via bronchoscopy.

People who have been infected but never developed active disease appear to be relatively more resistant to becoming reinfected with another strain i.e., they have partial immunity. Reinfection can however occur.

Brodie Fenlon, globeandmail.com: Could you tell us a bit more about why these cases of high-resistance TB are on the rise? Are there any clear strategies for fighting this upswing in MDR and XDR?

Dr. Michael Gardam: MDR and XDR can occur in one of two ways:

1. A person can start off with drug-sensitive TB and through a series of mishaps, take only some of their medications some of the time. When TB bacteria are only exposed to one drug at a time, the bacterial population rapidly become resistant to that antibiotic. Over time, if the intermittent therapy continues, a person can develop resistance to several classes of antibiotics. In the case of XDR TB, this process occurs over a longer period of time with many classes of antibiotics being used. Many of the MDR and XDR cases in the world arose this way.

2. A person with MDR or XDR TB can cough and infect somebody else with their resistant strain. The recent reports out of South Africa involving XDR TB showed that it was spreading person to person.

The strategies for addressing the first situation include making sure that all the drugs necessary are available for treatment and watching patients take their medication (a process called Directly Observed Therapy or DOT which is endorsed and promoted by the WHO). Often the mistakes that lead to MDR or XDR TB maybe due to the treating physician's inexperience in treating TB. It is not like other infectious diseases in that it requires very specific knowledge and treatment regimens.

The second situation requires the typical public health response involving isolating or quarantining patients who are infectious and improving the ventilation in settings where TB patients receive care. You can imagine a crowded outpatient clinic in the developing world with an XDR patient sitting in the waiting room in amongst patients with other disease, including HIV. Ironically the spread of TB through the healthcare system is one of the more frequent ways it can infect others. This was also seen in the 1990s in New York City where TB spread between AIDS patients while they were in clinics.

It is the natual tendancy of bacteria to become resistant to antibiotics -- we always play catch up. They are very genetically nimble and we have to be very careful when we use antibiotics that we are not simply selecting for resistant subpopulations of bacteria.

Brodie Fenlon, globeandmail.com: Thanks very much for sharing your expertise with us today, Dr. Gardam. Is there anything you would like to add in closing?

Dr. Michael Gardam: I think the take-home message about TB is that it is complicated! It spreads through the air and you have to breathe it in to get infected. When you become infected, you are infected for life. If you don't have any symptoms, you have latent infection whereas if you get sick, you have active disease. There are treatments for both of these states, and provided the bacteria is sensitive to antibiotics, they work very well. Drug-resistant TB is increasing in many parts of the world and it is only a matter of time before resistance rates start to increase in Canada. All this being said, TB remains a relatively rare disease in Canada hence most physicians will see very few cases in their lifetimes. This can result in unfamiliarity with the disease, and possible diagnostic or treatment challenges.