Tuberculosis in Canada: 1924-2012
Published by: The Public Health Agency of Canada
Issue: Volume 40-6: Tuberculosis
Date published: March 20, 2014
Volume 40-6, March 20, 2014: Tuberculosis
Tuberculosis in Canada: 1924-2012
Gallant V1, Ogunnaike-Cooke S1* and McGuire M1
1 Public Health Agency of Canada, Ottawa, Ontario
Background: Tuberculosis (TB) has been a notifiable disease since 1924 and remains an important and serious global public health challenge. Understanding the patterns and characteristics of TB are key to controlling and preventing further spread of the disease.
Objective: To provide an overview of national TB surveillance data collected through two national surveillance systems and to highlight important trends in recent years.
Methods: Trends in the incidence of TB since 1924 are presented. Descriptive results from the Canadian Tuberculosis Reporting System (CTBRS) and the Canadian Tuberculosis Laboratory Surveillance System (CTBLSS) are presented, with a focus on the years from 2002 to 2012. No statistical tests of significance were performed.
Results: Since the 1940s, both the number of reported TB cases and the overall Canadian incidence rate have declined. Males have always accounted for the greatest percentage of cases overall and individuals between the ages of 25 and 34 have typically accounted for the largest number of reported cases relative to other age groups. From 2002 to 2012, 66% of reported TB cases were foreign-born, but the highest burden of TB was in the Canadian-born Aboriginal population, with an average incidence rate five times that of the overall Canadian rate. Reported drug resistance in Canada remains consistently below international levels.
Conclusion: Overall, Canada has one of the lowest TB disease rates in the world. However, foreign-born individuals and Aboriginal people continue to be disproportionately represented among cases diagnosed in Canada. Surveillance systems like the CTBRS and CTBLSS are fundamental in providing information needed to target resources where they can be most effective.
The most recent report on tuberculosis (TB) by the World Health Organization (WHO) estimated that in 2012, 8.6 million people developed TB and 1.3 million died from the disease Footnote 1. As a result of improvements in general living conditions and overall population health Footnote 2, coupled with intensive efforts by the global Stop TB Strategy, the number of annual incident cases has been falling since 2006 Footnote 1.
A serious concern for TB prevention and control is TB drug resistance and the recent emergence of highly resistant strains which limit the available treatment options for those infected. In 2012, a WHO study revealed the highest ever global rates of multidrug-resistant tuberculosis (MDR-TB) cases Footnote 3.
The goal of this article is to provide a brief overview of the epidemiology of TB in Canada since reporting began in 1924, and to identify recent trends for the years 2002 to 2012. Data presented in this article should be considered in conjunction with two national surveillance reports: Tuberculosis in Canada 2012 - Pre-release Footnote 4, and Tuberculosis drug resistance in Canada 2012 Footnote 5.
TB surveillance in Canada
In Canada, active TB disease and TB drug resistance are monitored at the national level using two independent surveillance systems: the Canadian Tuberculosis Reporting System (CTBRS) and the Canadian Tuberculosis Laboratory Surveillance System (CTBLSS).
Canadian Tuberculosis Reporting System (CTBRS)
TB has been notifiable in Canada since 1924 and is currently legally reportable in all provinces and territories. Provincial and territorial public health authorities voluntarily submit data on TB cases that meet the case definition for national-level surveillance to the CTBRS on an annual basis.
The CTBRS, managed by the Public Health Agency of Canada (the Agency), is a case-based surveillance system which maintains selected non-nominal data on people diagnosed with active TB disease including, but not limited to, demographics (e.g. age, sex, immigration status), clinical and treatment information, diagnostic information, risk-factor information including HIV status, and treatment outcome details. The data are collected either through manual completion of a standard reporting form or by electronic transmission.
Canadian Tuberculosis Laboratory Surveillance System (CTBLSS)
The CTBLSS was established in 1998 to monitor TB drug resistance patterns in Canada. The CTBLSS is an isolate-based surveillance system and, like the CTBRS, the data for the CTBLSS are collected either through manual completion of a standard reporting form or by electronic transmission. Information requested includes sex, year of birth, province or territory from which the specimen originated, province or territory where the drug sensitivity testing was performed, and drug susceptibility results. Drug resistance develops when the strain of Mycobacterium tuberculosis causing the disease is resistant to one or more of the four first-line drugs (described below). In the CTBLSS, isolates are classified as either susceptible to all first-line medications, or resistant to one or more of the TB drugs.
The following resistance patterns are described in this article:
Mono-resistance – defined as resistance to one of the first-line drugs: isoniazid (INH), rifampin (RMP), ethambutol (EMB), or pyrazinamide (PZA).
Poly-resistance (other patterns) – defined as resistance to two or more first-line drugs, not including the INH and RMP combination.
Multidrug-resistant tuberculosis (MDR-TB) – defined as TB that is resistant to at least the two best first-line anti-tuberculosis drugs, INH and RMP, but which does not meet the definition of extensively drug-resistant TB (XDR-TB).
Extensively drug-resistant TB (XDR-TB) – defined as TB that is resistant to at least the two best first-line anti-tuberculosis drugs, INH and RMP, plus resistant to second-line drugs including any fluoroquinolone, and to at least one of three injectable second-line anti-tuberculosis drugs (amikacin, capreomycin, and kanamycin).
This article presents descriptive results from the CTBRS and the CTBLSS, primarily for the years from 2002 to 2012. Specifically, TB case counts and incidence rates are presented and are stratified by the following key variables where appropriate: reporting province or territory, age group, sex, origin status (defined as Canadian-born Aboriginal, Canadian-born non-Aboriginal and foreign-born) and diagnostic site. For drug resistance, the number and percentage of MDR-TB and XDR-TB cases are presented in addition to the total number of isolates tested. No statistical tests of significance were performed.
In the context of this article, the term "incidence" refers to new diagnoses of active TB in each reporting year. The WHO notes that "TB incidence has never been measured at national level because this would require long-term studies among large cohorts of people (hundreds of thousands) at high cost and with challenging logistics." Notifications of TB cases provide a good proxy indication of TB incidence in countries such as Canada, that have little underreporting of diagnosed cases and where the quality of and access to healthcare means that few cases are not diagnosed Footnote 1.
TB Trends in Canada, Over Time
After peaking in the 1940s, the number of reported TB cases and the corresponding rates declined rapidly
(Figure 1). Similarly, mortality from TB disease declined significantly. These declines were attributed to improved living conditions, better nutrition, and the introduction of effective medication in the mid-1940s. Deaths from TB appeared to outnumber new diagnoses each year during the 1920s. This may reflect incomplete reporting of all cases and of deaths among cases diagnosed in previous years, or it may indicate that reported cases reflected only hospitalized cases, whereas deaths captured all terminal cases of TB whether they were hospitalized or not. Systematic reporting of TB cases was instituted on a national basis in 1933, providing a more accurate and complete record of the burden of TB in Canada through the century.
Over the past two decades, both the number and rates of reported TB cases have continued to decline, albeit much more gradually than the drop observed from 1950 to 1990. In 1992, the rate was 7.7 per 100,000 population, which fell to an all-time low in 2010 at 4.7 per 100,000 population. The overall incidence rate increased slightly in 2012 to 4.8 per 100,000 population. This increase was attributed to two significant outbreaks in remote regions of northern Quebec and in Nunavut. These outbreaks are currently under control.
Figure 1: Reported tuberculosis incidence and mortality rates – Canada (1924-2012)
|Year||Incidence Rate||Mortality Rate|
Provincial and Territorial Distribution methods
Although the overall rate of TB in Canada continues to decline, the burden of disease is not shared equally across the country. On average, from 2002 to 2012, the three largest provinces (British Columbia, Ontario, and Quebec), which represent over 75% of the Canadian population, accounted for 72% of all reported cases. However, Nunavut, which represents less than 0.1% of the total Canadian population, reported 5% of all TB cases.
The reported incidence rates across the provinces and some territories have remained consistent for the past 11 years. In 2012, the Atlantic provinces, Ontario, Quebec, and the Yukon all reported incidence rates at or below the national rate of 4.8 per 100,000 population, whereas Alberta, British Columbia, and Saskatchewan reported rates above the national rate (ranging from 4.9 to 9.9 per 100,000 population), as did Manitoba and the Northwest Territories, with reported rates between 9.9 and 34.4 per 100,000 population. With the exception of two years, since becoming a separate territory in 1999, Nunavut has always reported the highest incidence rate of any province or territory. This trend continued in 2012, where the reported incidence rate for Nunavut was 234.4 per 100,000 population.
Table 1 provides the number of reported cases and the incidence rate broken down by province and territory for the years 2002 to 2012.
Sex and Age Distribution
The reported TB incidence rate has always been higher among males than females in Canada; from 2002 to 2012, 55% of all reported cases were males. During the same time period, individuals aged 25 to 34 years old represented the largest percentage of reported TB cases at 17%. Table 2 provides a breakdown of cases by age group for the years 2002 to 2012.
|Reporting Year||Canada||Age group|
Considering age and sex together, the largest burden of TB, as measured by the annual incidence rate, was in males 75 years of age or over (Figure 2).
Figure 2: Tuberculosis incidence rate by age group and sex – Canada (2012)
Bar chart of the reported tuberculosis incidence rate per 100,000 population in Canada for the year 2012, comparing males and females across the following age groups: less 1 year of age, between 1 and 4 years of age, between 5 and 14 years of age, between 15 and 24 years of age, between 25 and 34 years of age, between 35 and 44 years of age, between 45 and 54 years of age, between 55 and 64 years of age, between 65 and 74 years of age, and 75 and older.
Less than 1 year of age: male = 1.5, female = 3.2; between 1 and 4 years of age: male = 3.4, female= 2.8; between 5 and 14 years of age: male = 1.6, female = 1.3; between 15 and 24 years of age: male = 5.3, female = 5.0; between 25 and 34 years of age: male = 6.1, female = 6.0; between 35 and 44 years of age: male = 6.0, female = 5.3; between 45 and 54 years of age: male = 5.4; female = 3.3; between 55 and 64 years of age: male = 4.8, female = 2.1; between 65 and 74 years of age: male = 8.5 female = 4.1; 75 years of age and older: male = 14.5, female = 5.4.
Canadian-born Aboriginal people and foreign-born individuals are disproportionately represented among reported cases of active TB in Canada. A review of historical trends highlights changes in the epidemiology of TB by population group over time in Canada. From 1970 to 2012, years for which data on origin are available within the CTBRS, the proportion of active TB cases among the Canadian-born non-Aboriginal population decreased significantly, from 67.8% to 10.3%. During the same period, the proportion among foreign-born individuals increased from 17.7% to 65.3%, and the proportion among Canadian-born Aboriginal peoples increased from 14.7% to 22.5%
In 2002, the TB incidence rate for Canadian-born non-Aboriginal people was 1.0 per 100,000 population. This rate has fluctuated since then, but has remained steady at 0.7 per 100,000 population since 2010. The incidence rate for foreign-born cases was 20.0 per 100,000 in 2002, decreasing to a low of 13.4 per 100,000 in 2012. For Canadian-born Aboriginal people, the incidence rate was 22.0 per 100,000 population in 2002 and has since increased to 29.2 per 100,000 population in 2012.
In 2012, 10% of all reported cases in Canada were Canadian-born non-Aboriginal people, 23% were Canadian-born Aboriginal people, and 67% of cases were foreign-born.
The distribution of TB cases by affected population also varies by province and territory. In Alberta, British Columbia, Ontario, and Quebec, the majority of reported cases from 2002 to 2012 were foreign-born individuals (range: 60% to 90% of all reported cases), whereas in Manitoba, Saskatchewan, and the northern territories (Northwest Territories, Nunavut, and Yukon), Aboriginal people accounted for the majority of reported cases (range: 62% to 99% of all reported cases). In the Atlantic region (New Brunswick, Newfoundland and Labrador, Nova Scotia, and Prince Edward Island), close to half of all reported cases (46%) were Canadian-born non-Aboriginal people.
These varied geographic patterns, in part, reflect differences in population distribution within the provinces and territories in that there are more foreign-born individuals in Ontario, Quebec, British Columbia, and Alberta, whereas Aboriginal people make up a higher proportion of the population in the prairies and in the north.
Disease Type (Respiratory vs. Non-respiratory)
Active TB disease is classified as either respiratory or non-respiratory. Respiratory TB includes pulmonary TB, TB of the pleura, the intrathoracic or mediastinal lymph nodes, or of the larynx, nasopharynx, nose, or sinuses. Non-respiratory TB refers to all other disease sites Footnote 7.
From 2002 to 2012, 75% of all reported cases were diagnosed with respiratory TB. Of these, 87% (range: 82%to 89%) were diagnosed with pulmonary TB (which includes TB of the lungs and conducting airways) and 7% (range: 4.4% to 9.4%) were classified as "other TB respiratory disease". Within "other respiratory TB disease", pleurisy was the most frequently reported diagnosis, followed by TB of the intrathoracic lymph nodes. The remaining 6% (range: 3.9% to 8.8%) of respiratory cases were diagnosed with primary TB disease, a disease state which is characterized by pleuritis and pleural effusion, usually in an adolescent or young adult, but possibly in any age group, due to recent (within the preceding 24 months) infection with M. tuberculosis complex Footnote 7.
Twenty-four percent of the TB cases reported from 2002 to 2012 were classified as non-respiratory TB. Of these, 54% were diagnosed with peripheral TB lymphadenitis, 5% were diagnosed with TB of the central nervous system, and 2% were diagnosed with miliary or disseminated TB. The remaining 38% of cases were classified as "other" which includes primarily TB of the bones and joints, TB of the skin and subcutaneous cellular tissue, and TB of the intestines, peritoneum, and mesenteric glands.
Drug-resistant TB threatens TB control and is considered a major public health concern in several countries Footnote 1. Although drug-resistant TB, including MDR-TB and XDR-TB, has not yet been identified as a major problem in Canada, the potential for the emergence of more cases of drug-resistant TB in Canada exists due to the increase and ease of international travel.
From 2002 to 2012, a total of 14,880 isolates were tested for TB drug resistance. Of these, 176 (1.2%) were MDR-TB and seven (0.05%) were XDR-TB. Table 3 presents drug-resistance testing results for all isolates tested from 2002 to 2012.
|Year||Total number of isolates evaluated||MDR-TB* (%)||XDR-TB (%)|
|2002||1419||20 (1.4%)||1 (0.1%)|
|2003||1405||20 (1.4%)||1 (0.1%)|
|2006||1389||15 (1.1%)||1 (0.1%)|
|2008||1356||15 (1.1%)||1 (0.1%)|
|2010||1279||17 (1.3%)||1 (0.1%)|
|2011||1319||18 (1.4%)||1 (0.1%)|
|2012||1404||8 (0.6%)||1 (0.1%)|
|Total||14880||176 (1.2%)||7 (0.05%)|
*Does not include the XDR-TB
Overall, Canada has one of the lowest TB disease rates in the world, and reported drug resistance in Canada remains consistently below international levels. Available surveillance data highlight the unique aspects of TB in Canada, including the disproportionate effect on Aboriginal people and immigrants to Canada from areas of the world with high rates of TB disease.
Many affected Aboriginal communities are in remote and isolated regions of Canada Footnote 8 Footnote 9. Communities in the north often experience poor living conditions such as overcrowding and poorly ventilated housing. Some of these communities also suffer from poor nutrition, higher smoking levels, diabetes, and substance abuse Footnote 8 Footnote 9. These conditions put people at greater risk of TB disease Footnote 7. Recent outbreaks in remote areas of northern Canada have been the focus of much planning, and efforts to identify, diagnose, and screen all potentially infected individuals in an attempt to stop the ongoing transmission.
In 2012, foreign-born people represented over 65% of all reported TB cases and the majority of drug-resistant TB cases in Canada. Canada is a leading destination for migrants; in 2012 Canada received approximately 260,000 immigrants and refugees Footnote 10. Over the past 40 years, there has been a major demographic shift in the make-up of source countries of new migrants to Canada. Before the 1960s, most individuals immigrating to Canada came from European countries. Since the 1970s, however, most immigrants (more than 70%) come from countries in Asia, Africa, and Latin America, with intermediate or high TB incidence rates Footnote 11.
Strengths and Limitations of National TB Surveillance in Canada
TB surveillance in Canada is well established, but important limitations remain. Both the CTBRS and the CTLSS are passive surveillance systems which rely on data retrospectively gathered from medical records or laboratory results, as opposed to active surveillance involving prospective actions aimed at identifying cases. As a result, coverage of the system (i.e. whether all people with TB disease are being identified) is always a concern. The accuracy of the data is partially a function of timely reporting and updates to the Agency from the provinces and territories. Reporting delays do occur but rarely affect the final data. From 2002 to 2012, the WHO estimated the average case detection rate in Canada to be 85% (range: 75% to 98%) per year Footnote 1.
The methods used to collect and analyze the data presented in this article have been designed to minimize error. However, the data may be subject to coding, reporting, and processing errors that could not be detected or that were not corrected at the source. As an example, not all provinces and territories use ICD 9 or ICD 10 coding systems for recording disease diagnoses, a means that the CTBRS requires to classify patients according to the main diagnostic site.
With the CTBLSS, typically only isolates with MDR-TB or other extensive resistance patterns will receive drug-sensitivity testing to select second-line drugs. Although the Clinical and Laboratory Standards Institute recommends that INH mono-resistant isolates, as well as other poly-resistant, non-MDR isolates be tested for second-line drug resistance Footnote 12, this is not universally performed or reported on in Canada. Isolates other than MDR-TB may be resistant to a fluoroquinolone because of its widespread use for respiratory infections. This limits our understanding of the emergence of second-line drug resistance in Canada.
In Canada, the management and control of TB is complex. Remote Aboriginal communities that have experienced TB outbreaks challenge the health system's ability to provide adequate treatment in an effort to stop ongoing transmission of the disease and to resolve many social issues related to the spread of disease. In foreign-born populations, the challenge is to identify immigrant populations at high risk for progressing to active TB disease, including those that may be resistant to some of the best TB treatments available and require prolonged treatment. Surveillance systems like the CTBRS and CTBLSS are key to providing the health information needed to target resources where they can be most effective.
The authors would like to acknowledge the provincial and territorial tuberculosis programs and the Canadian Tuberculosis Laboratory Technical Network and their teams for their respective contributions to and participation in the CTBRS and the CTBLSS.
Conflict of Interest
The authors have no known conflicts of interests to declare.
This work was supported by the Public Health Agency of Canada.
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