Tuberculosis (TB) is a preventable and curable infectious disease, and yet it remains a significant global public health challenge.Footnote 1, Footnote 2 Each year, tuberculosis infects millions of people and is the second leading cause of death due to infectious diseases worldwide.Footnote 1 While the majority of TB cases and deaths occur in low- and middle-income countries, TB does exist in Canada.Footnote 1, Footnote 3, Footnote 4 During the first half of the twentieth century, TB was one of the leading causes of death and hospitalization; today, however, TB disease and death rates in Canada are low.Footnote 4-Footnote 6 Still, certain populations are disproportionately affected by TB, including the foreign-born and Canadian-born Aboriginal populations.Footnote 3, Footnote 4 As well, new treatment-resistant strains of TB are emerging.Footnote 7, Footnote 8 Efforts to reduce impact of this infection are ongoing.
Tuberculosis is an infectious disease caused by a group of bacteria, Mycobacterium tuberculosis complex.Footnote 9 There are two tuberculosis-related conditions: latent tuberculosis infection and active TB disease.Footnote 10-Footnote 12
Individuals with latent TB infection have been infected with the bacterium, but it is dormant and does not cause symptoms nor make the person infectious. In these cases, infection can be identified through a skin test or a blood test. Without treatment, a small proportion of these infected individuals will develop active TB disease in their lifetime.Footnote 8, Footnote 11, Footnote 13
Generally, latent TB infection develops into active disease as a result of weakened immune system, the existence of other health conditions or exposure to others with active TB. Active TB disease of the lungs is contagious, and individuals with active TB disease often feel sick and have a cough, pain in the chest area, experience weight loss or have a fever. TB can also affect the kidneys, spine, brain and lymph nodes. Persons with active TB require treatment.Footnote 8, Footnote 10, Footnote 12
TB is an infectious bacterium that is spread from person to person primarily through the air.Footnote 8, Footnote 9, Footnote 13 TB bacteria of the lungs or airways enter the air when a person with active TB disease exhales by coughing, sneezing, and even just talking.Footnote 8, Footnote 13 Once in the air, the bacteria can stay there for hours.Footnote 8, Footnote 13 Once an individual inhales them, the human body can react in one of three ways:
Many factors influence the development and spread of TB. Known risk factors for developing either latent TB infection or active TB disease include:
TB is a classic example of the relationship between an infectious disease and the social determinants of health.Footnote 16 A landmark study illustrated TB’s decline in the U.K. from 1838 to 1970, and attributed this decline primarily to improving social and economic conditions rather than clinical advances.Footnote 17 The research claims that, while effective medical interventions (e.g. antibiotics, chemotherapy) helped to reduce TB rates, those interventions were introduced only after TB rates were already in decline, and thus could not have been the main driving factor.Footnote 17 Rather, it was improvements to nutrition, hygiene, housing and working conditions in the post-industrial era that contributed most to the health progress achieved during this era.Footnote 17, Footnote 18
Figure 1 Reported tuberculosis incidence and mortality rates, Canada, 1924 to 2011Footnote 6
In Canada, the combination of the development and use of antibiotics coupled with social and infrastructure improvements have contributed to the dramatic drop in TB deaths and hospitalizations (Figure 1).Footnote 6, Footnote 19-Footnote 21 At the time of Canada’s Confederation, TB was considered the leading cause of death and the most important health problem facing Canadians.Footnote 5, Footnote 19, Footnote 22, Footnote 23 In 1944, streptomycin, the first anti-TB-specific antibiotic, was developed. By 1953, streptomycin was widely used in Canada.Footnote 24 Ten years after the wide use of antibiotics (streptomycin as well as others), the number of hospitalizations for TB was halved in Canada.Footnote 18-Footnote 21, Footnote 23, Footnote 24 However, Figure 1 shows that TB has not disappeared entirely in Canada and efforts to address TB are focused on a range of factors influencing transmission.
Reducing the impact of disease is dependent on addressing the underlying social and economic factors that drive the disease and influence its activation or re-activation.Footnote 16, Footnote 18 The WHO Commission on Social Determinants of Health suggests that interventions that are external to health-oriented interventions but that address social and economic conditions will have significant potential to strengthen future efforts against TB.Footnote 16, Footnote 25
March 24th is World Tuberculosis Day marking the discovery of the cause of the disease. By commemorating this day, the aim is to make the public aware that tuberculosis continues to be an epidemic in much of the world, causing the death of over a million people each year.Footnote 26
In 2011, there were approximately 8.7 million new cases and 1.4 million deaths associated with TB worldwide.Footnote 1 The estimated global incidence of TB is highest in Asia and Africa, with India and China together accounting for almost 40% of the world’s TB cases.Footnote 1
Part of the United Nation’s sixth Millennium Development Goal to combat HIV/AIDS, malaria and other diseases is to halt and begin to reverse the global TB epidemic by 2015.Footnote 27 The number of new TB cases fell by 2.2% between 2010 and 2011, and since 1990, the TB mortality rate has decreased by 41%, indicating that progress is being made towards reaching the global target goal of a 50% reduction in TB deaths by 2015.Footnote 1 Nevertheless, the global burden of TB remains high. Canada has a role to play in reducing the global burden as a participant in international health efforts and in addressing TB among Canada’s foreign-born population.
Figure 2 Reported new active and re-treatment tuberculosis cases by place of birth, Canada, 2011Footnote 3
With 1,607 new active and re-treatment (latent) TB cases reported to the Canadian Tuberculosis Reporting System in 2011, TB is no longer common in the overall Canadian population.Footnote 3 However, although the overall rate is low (4.7 per 100,000), TB is disproportionately distributed among specific sub-populations.Footnote 3 Of all the reported TB cases in 2011, 67% were among foreign-born individuals, 19% were among Canadian-born Aboriginal individuals, 12% were among Canadian-born non-Aboriginal individuals, and 2% were of unknown origin (see Figure 2).Footnote 3
Canada’s provinces with the largest population—British Columbia, Ontario and Quebec—have the largest total number of TB cases representing 70% of TB cases, in 2011.Footnote 3 The majority of the cases were among foreign-born individuals as a result of a larger influx in these regions.Footnote 3 Although the population is smaller, rates of TB are much higher in northern regions (generally including regions in the territories and northern portions of some provinces).Footnote 3 In 2011, Yukon reported 11.5 cases per 100,000 population, Northwest Territories reported 29.8 cases per 100,000 population and Nunavut reported 222.1 cases per 100,000 population.Footnote 3 The majority of cases in Manitoba and Saskatchewan were also primarily located in their northern regions and were among Canadian-born Aboriginal people.Footnote 3 For example, 76% of Saskatchewan’s active and re-activated TB cases were in northern Saskatchewan, an area that represents only 3.5% of that province’s population.Footnote 28 In the Atlantic region in 2011, the majority of reported TB cases are among foreign-born or Canadian-born non-Aboriginal populations.Footnote 3
In 2011, people who were foreign-born accounted for the majority of new active and re-treatment TB cases in Canada.Footnote 3 Although the overall number of reported cases has not increased significantly since 1970, the proportion of the foreign-born population with TB infection or disease has increased.Footnote 4 About 80% of Canada’s foreign-born population with TB originated from high TB-incidence regions such as Africa; the western Pacific and southeast Asia (defined WHO regions).Footnote 3 Those with latent TB infection are more likely to develop active TB disease within 5 years after arrival.Footnote 4, Footnote 29, Footnote 30 Not enough is known about the foreign-born population and the influence of their social and economic determinants of health. Limited data continue to be a public health challenge in addressing TB in this population.
Despite the overall low incidence of TB in Canada, the burden of TB in the Aboriginal population is much greater than in the overall population.Footnote 14, Footnote 31 The Aboriginal population is about 4.3% of the total Canadian population but accounts for about 19% of estimated TB disease burden.Footnote 3, Footnote 32 In 2011, the incidence rate of active TB disease reported for the Canadian-born Aboriginal population was 34 times higher than for the Canadian-born non-Aboriginal population.Footnote 3, Footnote 32
Figure 3 Reported new active and re-treatment tuberculosis cases by Aboriginal status, Canada, 2011Footnote 3
In 2011, the overall rate of TB infection and disease among Canadian-born Aboriginal people was nearly six times the overall Canadian rate (23.8 per 100,000 population compared with 4.7 per 100,000 population) and higher than the rate among foreign-born people (13.5 per 100,000 population).Footnote 3 Figure 3 shows that the highest TB rate was found among Inuit at 177.6 per 100,000 population, followed by First Nations living on a reserve (20.5 per 100,000 population); First Nations not living on a reserve (15.7 per 100,000 population); and Métis (6.0 per 100,000 population).Footnote 3 The numbers do reflect the burden of TB in some of these remote communities. For example, the overall Inuit population is small and therefore minimal changes in the number of cases can substantially alter rates. The incidence rates of TB disease vary across four Inuit regions (Inuvialuit [northern section of the Northwest Territories], Nunavut, Nunavik [across northern Quebec] and Nunatsiavut [northern Labrador]).Footnote 33 In 2011, the incidence of TB disease was much higher in Nunavik and Nunavut compared to Inuvialuit and Nunatsiavut which had low numbers.Footnote 33
Several factors are believed to affect TB rates in Aboriginal communities. These include historical context, other health conditions, environmental conditions and challenges related to the health system.Footnote 4, Footnote 14, Footnote 31, Footnote 33-Footnote 36 The historical context is particularly relevant. Before contact with Europeans, TB infection did not exist in Aboriginal communities. The creation of trade and work relationships (such as development of the western railway in the late 19th century) and the establishment of the reserve system changed the structure of Aboriginal societies and increased risk factors for the development and spread of TB.Footnote 36-Footnote 38 Living on reserves, in villages and residential schools, with crowded living conditions and malnutrition, fostered the progression of TB infection to active disease.Footnote 4, Footnote 19, Footnote 36 Children in residential schools were particularly at risk due to the living conditions associated with dormitories and malnutrition.Footnote 4, Footnote 36
There is evidence of TB infection within Aboriginal populations that has existed over generations.Footnote 4, Footnote 36, Footnote 38 Previous TB infection or disease becomes activated or re-activated (often as a result of social and economic conditions such as limited access to medical practices, inadequate housing and other underlying illnesses) and exposes a new generation to TB infection. Molecular evidence shows that most TB in Canada stems from reactivation of disease.Footnote 4, Footnote 36
There is also a history of community loss and displacement related to TB prevention and control practices. Aboriginal family members with active TB disease, particularly Inuit, were often transferred for treatment in sanitoria in the south. Many did not return to the communities and often the bodies of the deceased were often not returned to their families or communities. The legacy of these practices has adversely influenced communities and affected the social acceptance of prevention and treatment.Footnote 33, Footnote 35
Other conditions that are risk factors for progression of latent TB infection to active TB disease are also prevalent in some Aboriginal communities. These include diabetes, malnutrition, HIV infection and substance use.Footnote 4, Footnote 35, Footnote 36 For example, diabetes, a recognized risk factor for TB development, is about three to five times more prevalent in the First Nations population than the overall Canadian population.Footnote 4 HIV is also a strong risk factor for TB (see “TB and HIV co-infection”), and new reported cases of HIV are increasing the risk for TB comorbidity.Footnote 4
Social and environmental factors can increase the risks of transmission, infection and the progression from latent infection to active disease. For example, living in inadequate, poorly ventilated and overcrowded housing can cause increased risk of exposure to TB infection and progression to TB disease.Footnote 39 Poor housing conditions are disproportionately high in Aboriginal communities.Footnote 31, Footnote 35, Footnote 39 Compared to non-Aboriginal Canadians, First Nations people living on a reserve have higher household occupancy density and poorer housing conditions (e.g. air quality, ventilation).Footnote 39 As well, living in remote communities limits access to services and nutritious foods.Footnote 35, Footnote 40
The healthcare system for TB prevention and control in Aboriginal communities can be complex.Footnote 35, Footnote 36 The system is multijurisdictional as provinces/territories, federal departments and agencies, First Nations and Inuit organizations and local communities are involved in delivering TB prevention and control programs to communities. Complex systems are often associated with challenges in coordinating and efficiently delivering services.Footnote 35 Remoteness in terms of access to expertise, testing facilities and medications further challenges the delivery of service. Periods of infectiousness and illness can be prolonged by delays in diagnosis and interruptions in treatments as well as increasing resistance to typical treatments.Footnote 4, Footnote 35 Distance to services, diagnostics, laboratories and medication suppliers can influence how local social services and healthcare providers collaborate and communicate.Footnote 4
To significantly reduce the incidence and burden of TB among First Nations living on a reserve, Health Canada worked in collaboration with First Nation and Inuit organizations and communities, federal and provincial partners and TB experts to develop the Strategy Against Tuberculosis for First Nations On-Reserve in 2012.Footnote 35 There are three themes to this strategy:
In 2013, the Inuit-Specific Tuberculosis (TB) Strategy was released by Inuit Tapiriit Kanatami (in collaboration with the National Inuit Committee on Health and the Inuit Public Health Task Group) to focus on the need for effective approaches for TB prevention, control and care in order to address the disproportionate burden of TB disease among Inuit compared to the overall Canadian population.Footnote 33 The disparity is believed to be rooted in a number of influencing factors including the social and economic determinants of health. The strategy aims to increase awareness about TB rates among Inuit populations, the factors influencing those rates, and to guide stakeholders and partners in developing a holistic TB action plan that is culturally appropriate and sustainable.Footnote 33
The Canadian Institutes of Health Research (CIHR) funds research that bridges scientific knowledge and traditional knowledge of First Nations, Inuit and Métis peoples to help identify health interventions that work. The CIHR Pathways to Health Equity for Aboriginal Peoples is a forward-looking funding program developed to increase the understanding of Aboriginal health inequalities and how to address them.Footnote 41 This initiative aims to address four timely and important health inequities affecting First Nations, Inuit and Métis peoples: TB, obesity, suicide and oral health.Footnote 41
Without receiving appropriate and timely treatment, two-thirds of the world’s population with TB disease will die.Footnote 1, Footnote 2 Overall, the global goal of TB treatment is to reverse incidence of TB in the period of a lifetime.Footnote 1 In this context, there has been much success as 85% of all newly diagnosed cases were successfully treated in 2010.Footnote 1 However, more can be done.
Public health programs rely on combined and collaborative practices that include implementing standards and guidelines, enlisting cross-sectoral collaboration and engaging public commitment to manage disease. In Canada, the public health role has two parts: the infrastructural and the operational aspects.Footnote 4 Addressing TB in Canada is a shared responsibility between the federal government and the provinces and territories. Each jurisdiction has legislation that requires reporting data, diagnostics and test results of all TB cases. In areas with high rates of TB, trained teams offer primary medical and social support and address specific risks of HIV co-infection. A high priority for TB control programs is to identify cases and trace the spread of disease.Footnote 4 Commitment to address TB also relies on public understanding of the severity of the issue and the need for action. Raising awareness and educating Canadians on TB, its origins, causes, symptoms and need for treatment is important to reducing the number of future cases.Footnote 4 Practices such as the Inuit Strategy are working to increase awareness and knowledge of the burden of TB in Inuit communities.Footnote 33
Immunization was used as a TB prevention and control mechanism in Canada.Footnote 42 The Bacille Calmette-Guérin (BCG) vaccine was developed in the 1920s and was given to babies and young children to protect them against the most severe strains of active TB disease.Footnote 42, Footnote 43 In Canada, BCG was widely used from the 1920s until anti-TB medications were more widely used and TB incidence decreased.Footnote 4, Footnote 44 BCG as a prevention tool has had mixed results. In Canada, its widespread use has been mostly discontinued except in certain circumstances.Footnote 4, Footnote 33-Footnote 35, Footnote 44 For example, in order to reduce risks to children, Nunavut administers BCG to all newborns, and in the Northwest Territories, BCG is available to infants in TB-endemic regions or communities.Footnote 33
Today, several antibiotics are used to treat latent and active TB disease.Footnote 4, Footnote 45 Treatment of active TB disease takes months.Footnote 4, Footnote 45, Footnote 46 During the initial intensive phase, a combination of (usually) four doses are administered to destroy rapidly replicating Mycobacterium tuberculosis bacteria and to prevent the development of antimicrobial resistance.Footnote 4 During the continuation phase, the number of treatments used are reduced and the focus is on killing the remaining, slowly replicating, bacteria.Footnote 4 The antibiotics used to kill these TB bacteria only work when the TB bacteria are growing.Footnote 4, Footnote 46 Treatment of latent TB infection is also recommended for those with an increased risk of TB to reduce the chances of it developing into active TB disease.Footnote 4, Footnote 47 Effective treatment is only possible with the maintenance of treatment plans.
Antimicrobial resistance occurs when the micro-organism that causes disease is no longer susceptible to the medications available to treat it (see “Antimicrobial Resistance—A Shared Responsibility”).Footnote 48, Footnote 49 If a person receiving TB treatment stops taking the prescribed medication before the end of treatment or does not take it as directed, the TB may become resistant, and, as a result, difficult to treat.Footnote 8, Footnote 46, Footnote 50 There is also the risk of spreading the antimicrobial-resistant strains of TB to others.Footnote 8, Footnote 46
Strains of Mycobacterium tuberculosis are becoming increasingly resistant to anti-TB treatments—especially in areas where TB control programs have been less effective.Footnote 1 Multidrug-resistant Mycobacterium tuberculosis (MDR-TB) strains are resistant to at least two of the most effective first-line treatments, isoniazid and rifampin.Footnote 1, Footnote 7 In these cases, alternate treatments that are more costly, usually have more reported side effects, and may be less effective as the first-line treatment that needs to be taken.Footnote 1, Footnote 50 The number of cases of MDR-TB reported in the countries with the highest burden of TB has almost doubled between 2009 and 2011.Footnote 1 In 2011, nearly 60,000 cases of MDR-TB were reported globally to the World Health Organization (WHO)—one in five (19%) of the confirmed TB cases.Footnote 1 About one-third of MDR-TB patients may die each year.Footnote 51 In 2011, 18 cases of MDR-TB were reported in Canada.Footnote 7
Extensively drug-resistant Mycobacterium tuberculosis (XDR-TB) strains are resistant not just to isoniazid and rifampin but also to most of the alternatives used to treat MDR-TB.Footnote 7 In 2011, XDR-TB had been confirmed in 77 countries.Footnote 51 Since the Canadian Tuberculosis Laboratory Surveillance System began testing for XDR-TB in 1998, 234 isolates have been classified as MDR-TB and 6 as XDR-TB.Footnote 7 While XDR-TB is not yet a major problem in Canada, it is a growing international concern.Footnote 7
Globally, TB is among the most common cause of infection and death for those living with HIV.Footnote 2, Footnote 52, Footnote 53 About one-third of those living with HIV worldwide are also co-infected with TB, while in 2011, an estimated 13% of all new TB cases were co-infected with HIV.Footnote 1, Footnote 2, Footnote 53 However, this estimate varies by region and is much higher in HIV-endemic regions such as sub-Saharan Africa where about 70% of those with TB are also infected with HIV.Footnote 53 Co-infection with TB can also accelerate the progression of HIV infection to AIDS.Footnote 2, Footnote 53
The risk of developing TB increases when the immune system is weakened. Since HIV weakens and destroys immune systems, being HIV-positive increases a person’s vulnerability to TB and HIV can accelerate the progression of latent TB to active disease.Footnote 53 While co-infection can occur at any stage, the risk of TB co-infection increases as immune suppression advances. The use of anti-retroviral and/or preventive TB therapy is believed to be a cost-effective alternative to treatment after TB infection causes disease.Footnote 53 As TB and HIV share common social and economic risk factors, addressing these determinants of health would also be effective.Footnote 25
Early identification, diagnosis and treatment of TB is important for all but particularly for those who are HIV positive.Footnote 4, Footnote 54 Newly diagnosed HIV infections should be assessed for likelihood of exposure to TB (e.g. living in close contact with individuals with known or suspected TB).Footnote 4, Footnote 15 Globally, only about 2.4% of people living with HIV and AIDS are actually tested for TB.Footnote 53 Even with screening, identifying the disease can be difficult as much of TB testing focuses on lungs when TB infection of other sites of the body is also possible.Footnote 1, Footnote 53 Regardless, healthcare professionals should be watchful of suspicious cases.Footnote 4, Footnote 54 As well, the Canadian Tuberculosis Standards recommended that people diagnosed with TB should also be assessed for HIV infection.Footnote 4
Treating the TB infection and disease is critically important to those living with HIV, but can be complicated due to interactions between medications. Medications used to treat HIV can affect TB treatment; and medications used to treat TB can decrease the effectiveness of HIV treatment. Antimicrobial-resistant TB further complicates treatment for those living with a range of co-infections.Footnote 1, Footnote 4
Public health programs and health services for TB control must be coordinated within HIV and AIDS programs because of the frequency of dual infection. In areas with high TB infection rates, people with HIV infection should be monitored for TB. Since those living with HIV are likely to experience symptoms or realize they have been exposed before seeing a healthcare provider, ongoing prevention and health promotion programs that raise awareness about the risks of co-infection are necessary in HIV support programs.Footnote 1, Footnote 54
Given the rates of TB among foreign-born Canadians and the number of Canadians travelling abroad, Canada also has a role to play in the global reduction of TB and, in particular, the reduction of TB and HIV co-infection. Canada must continue to collaborate with partners in organizations such as the Global Fund to Fight AIDS, Tuberculosis, and Malaria, the Stop TB Partnership (e.g. Global Drug Facility, TB Reach) and WHO.Footnote 1, Footnote 55-Footnote 58 As a result of these programs, progress has been made towards achieving the aforementioned 2015 Millennium Development Goals.Footnote 27, Footnote 59 Canada supports international efforts in the fight against tuberculosis. The Economic Action Plan 2013 reaffirms Canada's commitment to expanding prevention, care and treatment for those most vulnerable.Footnote 59-Footnote 61
Tuberculosis continues to be a global health problem. TB is preventable and treatable but still kills many people each year. While Canada’s overall rates are low and continue to decline, challenges remain. High rates among the foreign-born population show that Canada is not isolated from the global burden. As well, unacceptably high rates of TB persist among Aboriginal populations persist and, in some cases, have increased. In addition, those who are immune-compromised or who are HIV positive are at increased risk of TB co-infection. Antimicrobial resistance has challenged traditional treatment options. Canada needs to be ever more vigilant in its prevention and control efforts to mitigate the spread of TB in the future.