Results: Tuberculosis in Canada 2012 – Section I: TB Case Reporting

Results

Section I – TB Case Reporting

Background: Historical context

In Canada, the number of reported TB cases and the corresponding incidence rates peaked in the 1940s and fell rapidly until the 1980s at which point the decline in the rates moderated and then stabilized. Similarly, the reported number of deaths (before or during treatment) among those diagnosed with active TB disease fell at a constant and rapid rate. The decline in both the number of reported cases and the number of reported deaths can be attributed to improved living conditions, better nutrition, and the introduction in the 1940s of effective anti-tuberculosis medication (Figure 1).

Figure 1: Tuberculosis incidence and mortality rates and year of first-line antimicrobial tuberculosis drug introduction – Canada: 1924-2012

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The number of reported cases and the TB incidence rate has consistently been higher for males than for females.

An important trend over time has been the change in the profile of reported TB cases in Canada with respect to origin. In 1970, of the 4,538 reported cases, the majority were Canadian-born non-Aboriginal people (68%); 18% were foreign-born and 14% were Canadian-born Aboriginal people. Immigration patterns over the past 40 years have changed, resulting in a major demographic shift in the source countries of new migrants to Canada. Before the 1960s, most individuals immigrating to Canada came from European countries. However, since the 1970s most immigrants (more than 70%) have come from countries in Asia, Africa, and Latin America, recognized by the WHO as high-burden TB countries (data are not shown).

The foreign-born now comprise the largest percentage of all reported TB cases in Canada (Figure 2). Still, ongoing TB transmission among Canadian-born Aboriginal people continues to be an important challenge to TB control in Canada. Based on incidence rates, the Canadian-born Aboriginal population carry the highest burden of TB disease in Canada.

Figure 2: Percentage of reported tuberculosis cases by origin – Canada: 1970-2012

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Case Reporting for 2010, 2011, and 2012

From 2002 to 2012, both the number of reported TB cases and the corresponding incidence rates have remained relatively unchanged. In 2002, there were 1,667 reported cases of TB for a corresponding incidence rate of 5.3 per 100,000 population. From 2010 to 2012, 4,890 new active and re-treatment TB cases were reported to the CTBRS: 1,587 cases in 2010, 1,618 cases in 2011, and 1,685 cases in 2012. By 2010, the incidence rate had decreased marginally to 4.7 per 100,000 population. In 2011, the incidence remained the same at 4.7 per 100,000, and in 2012, the incidence rate was 4.8 per 100,000 population (Figure 3; Table 1A). Of note, there were two outbreaks in remote regions of northern Quebec and in Nunavut in 2011 and 2012.

Of the 1,685 cases reported in 2012, 1,570 (93%) were new active TB cases and 91 (5%) were re-treatment cases (defined as having had at least one previous diagnosis of TB disease in the past) (Table 1B and Table 1C). Previous history of TB disease was unknown for 2% of the reported cases.

Figure 3: Reported number of tuberculosis cases and incidence rate per 100,000 population – Canada: 2002-2012

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Province and territory

From 2002 to 2012, the incidence rates across the provinces remained relatively stable. From 2010 to 2012, at least one case of TB was reported each year in each province and territory. Six provinces and territories reported more cases in 2012 than in 2011, and one reported the same number. The remaining five jurisdictions reported fewer cases in 2012 than in 2011 (Table 1A).

In 2012, the three largest provinces (British Columbia, Ontario, and Quebec), which comprised 75% of the total Canadian population, accounted for the majority of all reported TB cases (69%) in Canada (Table 1A).  However, Nunavut, which represented 0.1% of the Canadian population, reported 5% percent of all TB cases. In 2012, incidence rates in the Atlantic provinces (New Brunswick, Newfoundland and Labrador, Nova Scotia, and Prince Edward Island), Ontario, Quebec, and Yukon were all equivalent to or below the Canadian rate of 4.8 per 100,000 population, whereas all other provinces and territories reported rates above the Canadian rate. The incidence rate has consistently been high in Nunavut and this trend continued in 2012, where the incidence rate was 234.4 per 100,000 population (Figure 4; Table 1A).

Figure 4: Tuberculosis incidence rate per 100,000 population by province/territory: 2012

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Age and sex

In 2012, individuals aged 25 to 34 years old represented the largest percentage of reported cases (17%). However, the highest incidence rate was observed for those aged 75 years or older, at 9.1 per 100,000 population (Figure 5; Table 2A).

An important measure of TB control is the incidence of active TB disease in children under 15 years of age since these cases may represent recent ongoing transmission of TB.  In 2012, 6.5% of reported cases were less than 15 years of age (Table 2A).

Figure 5: Tuberculosis incidence rate per 100,000 population, by age group – Canada: 2012

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In 2012, males accounted for 983 (58%) of all reported TB cases, corresponding to an incidence rate of 5.7 per 100,000 population, whereas females accounted for 702 (42%) of the reported cases, for a corresponding incidence rate of 4.0 per 100,000 population (Figure 6; Table 2B and 2C).

Figure 6: Tuberculosis incidence rate per 100,000 population, by sex – Canada: 2002-2012

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In 2012, TB incidence rates were similar for males and females between birth and 44 years of age, after which the incidence rate was higher for males compared to females. For those aged 75 years and older, the incidence rate for males (14.5 per 100,000 population) was almost three times higher than the rate for females (5.4 per 100,000 population) (Figure 7; Table 2B and 2C). The distribution of cases by sex and age was similar from 2002 to 2012.

Figure 7: Tuberculosis incidence rate per 100,000 population, by age group and sex – Canada: 2012

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Origin

Overall, Canada has one of the lowest TB disease incidence rates in the world.Footnote 4 However, the burden of disease is not shared equally across the three major origin groups: Canadian-born Aboriginal people; Canada-born non-Aboriginal people; and the foreign-born. In particular, Canadian-born Aboriginal people and foreign-born individuals continue to be over-represented among TB cases in Canada.

From 2002 to 2012, the distribution of cases across origin groups has remained relatively unchanged (Figure 8; Table 4). However, from 2002 to 2012, the incidence rate for the Canadian-born Aboriginal population increased from 22.0 to 29.2 per 100,000 population. In comparison, the incidence rate for the foreign-born population decreased from 20.0 per 100,000 population in 2002 to 13.4 per 100,000 in 2012. In 2002, the incidence rate for Canadian-born non-Aboriginal people was 1.0 per 100,000 population. This rate has fluctuated little since then and has remained steady at 0.7 per 100,000 population since 2010 (Figure 9; Table 4).

Figure 8: Percentage of reported tuberculosis cases by origin – Canada: 2002-2012

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Figure 9: Tuberculosis incidence rate by origin – Canada: 2002-2012

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In 2012, the foreign-born population, which represented 24% of the total Canadian population, accounted for 65% (n=1,100) of all reported cases. Canadian-born Aboriginal people made up 4% of the total Canadian population but accounted for 22% (n=379) of the reported cases. Despite making up the majority of the Canadian population, in 2012 Canadian-born non-Aboriginal people accounted for the lowest percentage of reported cases at 10% (n=173) (Figure 9; Table 4).

The distribution of TB cases across origin groups varied by reporting province and territory. In 2012, the majority of cases reported by Alberta, British Columbia, Ontario, Prince Edward Island, and Quebec were foreign-born. Compared to previous years, in 2012, a higher percentage of cases diagnosed in Quebec were Canadian-born Aboriginal people. This was partially attributed to TB outbreaks in remote northern communities of the province. Canadian-born Aboriginal people accounted for the majority of reported cases in Manitoba and Saskatchewan. In the territories (Northwest Territories, Nunavut, and Yukon), all reported cases were Canadian-born Aboriginal people. In New Brunswick, Newfoundland and Labrador, and Nova Scotia, the majority of reported cases were Canadian-born non-Aboriginal people (Figure 10; Table 5).

Figure 10: Percentage of reported tuberculosis cases by origin – Canada, provinces and territories: 2012

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In general, Canadian-born Aboriginal cases were younger than both the foreign-born and Canadian-born non-Aboriginal cases whereas more than one-half of Canadian-born non-Aboriginal cases were adults aged 45 or older. In 2012, approximately one-third of the Canadian-born Aboriginal cases and the Canadian-born non-Aboriginal cases were younger than 25 years of age, whereas 14% of the foreign-born cases were younger than 25 years of age. Fifty percent of the Canadian-born Aboriginal cases and 50% of the foreign-born cases were between 25 and 54 years of age compared with 25% of the Canadian-born non-Aboriginal cases. Among Canadian-born Aboriginal cases, 7.4% were aged 65 years or older whereas 30% of the Canadian-born non-Aboriginal cases and 27% of the foreign-born cases were aged 65 or older (Figure 11; Table 6-3).

Figure 11: Percentage of reported tuberculosis cases by age group and origin – Canada: 2012

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Of the 1,100 foreign-born cases reported in 2012, the year of arrival into Canada was known for 97% of cases. Of these, 7% arrived in 2012, 12% in 2011, and 19% of the cases arrived between 2008 and 2010, that is, within two to five years of being diagnosed with active TB disease in Canada (Table 7).

In 2012, immigration status at the time of diagnosis was reported for 68% of the 1,100 reported foreign-born cases. Of these, at the time of diagnosis, 80% were reported to be Canadian citizens or permanent residents, 6% were refugees, refugee claimants or convention refugees, and 7% were temporary residents (visitors, students or foreign workers). For the remaining 7% of reported TB cases, immigration status was reported as “other” without additional details (Table 8).

Aboriginal populations

Canadian-born Aboriginal people comprise three distinct populations: First Nations people, Inuit, and Métis people. In 2012, of the 379 reported Canadian-born Aboriginal cases, 208 (55%) were First Nations, 160 (42%) were Inuit, and 11 (3%) were Métis. In 2012, the incidence rate in the Métis population was 3.1 per 100,000 population, which was lower than the overall Canadian incidence rate of 4.8 per 100, 000 population. By comparison, the incidence rate in the First Nations population, at 23.7 per 100,000 population, was almost five times the overall Canadian rate. However, the highest incidence rate was observed for the Inuit population, at 262.2 per 100,000 population. With the exception of 2003, from 2002 to 2012, the annual incidence rates for the Inuit were the highest of any origin group in Canada (Table 4).

Foreign-born cases by WHO epidemiological region

Based on country of birth, foreign-born cases can be grouped into one of nine epidemiological regions as defined by the STOP-TB Partnership/WHO TB (Appendix 6)^{Footnote 5}:

• Established Market Economies (EME) and Central Europe (CEUR)
• Africa, high HIV prevalence (AFR-High)
• Africa, low HIV prevalence (AFR-Low)
• American Region – Latin American countries (AMR)
• Eastern European Region (EEUR)
• Eastern Mediterranean Region (EMR)
• South-East Asian Region (SEAR)
• Western Pacific Region (WPR)

From 2002 to 2012, 11,942 cases were foreign-born individuals, accounting for 66% of all reported TB cases in Canada, and representing more than 170 countries of origin. Figure 12 shows the percentage of foreign-born TB cases in Canada by the respective epidemiological region of birth from 2002 to 2012. During this period, approximately 40% of all the reported foreign-born cases originated from the WPR, and this has remained stable over the 11-year period.

Figure 12: Percentage of foreign-born tuberculosis cases by WHO TB epidemiological region – Canada: 2002-2012

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Similarly, in 2012, individuals born in the WPR countries accounted for the highest percentage of reported foreign-born cases in Canada (42%). These cases were primarily from the Philippines, China, and Vietnam. However, the highest incidence rate, at 38.9 per 100,000 population, was observed for foreign-born individuals from the AFR-High region, primarily Ethiopia and Nigeria (Table 5-3). As shown in Figure 13 below, when the foreign-born cases in Canada are grouped according to the nine WHO epidemiological regions (Appendix 6), incidence rate patterns in Canada mirrored the incidence rate patterns in the regions themselves, with the AFR-high region reporting the highest rate and the EME-CEUR region reporting the lowest.

Figure 13: Comparison of the foreign-born tuberculosis incidence rate per 100,000 population in Canada grouped by STOP-TB Partnership/WHO TB epidemiological region of birth with WHO-estimated tuberculosis incidence rate per 100,000 population in each region

Disease type and diagnostic classification

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. Primary disease^{Footnote iv} is also captured under the respiratory classification. Non-respiratory TB refers to all other disease sites.^{Footnote 6} Similar to previous reporting years, of the cases reported in 2012, 77% were diagnosed with respiratory TB and 23% with non-respiratory TB (Table 9).

Pulmonary TB, including TB of the lungs and conducting airways, accounted for the majority (68%) of reported cases in 2012 (Table 9). Of the remaining cases:

• approximately 6% were classified as “other TB respiratory disease” which included tuberculous pleurisy (non-primary) and tuberculosis of the intrathoracic lymph nodes, mediastinum, nasopharynx, nose (septum), and sinus (any nasal)
• 4% were classified as having primary TB disease
• 12% were classified as TB of the peripheral lymph
• 9% were classified as “other,” which includes TB of the intestines, peritoneum and mesenteric glands, bones and joints, genitourinary system, skin, eye, ear, thyroid, adrenal, and spleen
• approximately 1% were diagnosed with TB of the meninges and central nervous system (CNS)
• less than 1% were diagnosed with miliary TB

In 2012, pulmonary disease accounted for the highest percentage of all reported TB cases across all age groups and origins. A higher percentage of primary cases were diagnosed among those under the age of 15 years (Table 11-3).

In 2012, for both the Canadian-born Aboriginal and Canadian-born non-Aboriginal cases, primary disease accounted for 9% of the reported cases. In the foreign-born, less than 1% of reported cases were diagnosed with primary TB (Figure 14; Table 12-3).

Of the cases diagnosed with peripheral lymph node disease, 186 (91%) were foreign-born, compared to 2% in the Canadian-born Aboriginal population and 5% in the Canadian-born non-Aboriginal population (Figure 14; Table 12-3).

Figure 14: Reported number of tuberculosis cases by main diagnostic classification and origin – Canada: 2012

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History of previous TB disease

Of the 1,685 cases reported in 2012, 91 (5%) were re-treatment cases (defined as having had at least one previous diagnosis of TB disease in the past) (Table 1-C). Previous history of TB disease was reported as unknown for 2% of the reported cases. Of the reported re-treatment cases, 50 (55%) were foreign-born, 31 (34%) were Canadian-born Aboriginal people, and nine (10%) were Canadian-born non-Aboriginal people.

In 2012, the date of previous diagnosis was reported for 69 (76%) of the 91 reported re-treatment cases. Of these, seven cases (10%) developed active TB within two years of the previous episode, and 19 (28%) cases developed active TB within five years of the previous episode. For over half (58%) of the re-treatment cases, the previous diagnosis was more than 10 years prior to the current episode (Table 14).

Laboratory confirmation

From 2002 to 2012, approximately 28% of all reported cases were smear-positive pulmonary TB cases; among pulmonary TB cases during this same time period, 43% were smear-positive (Figure 15).

Figure 15: Percentage of pulmonary cases by sputum smear microscopy results – Canada: 2002-2012

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In 2012, 83% of reported cases were laboratory-confirmed, which includes all smear- and culture-positive cases (Table 15-3). Of the 1,138 reported cases of pulmonary TB in 2012, approximately half (48%) were microscopy- (smear-) positive, denoting probable infectious pulmonary TB (Table 17-3).

Initial drug resistance

Phenotypic drug susceptibility testing (DST) is recommended for all first culture-positive TB isolates obtained from each new TB case.^{Footnote 6}

This report describes the following drug-resistance patterns:

• monoresistance - resistance to one of the first-line drugs: isoniazid (INH), rifampin (RMP), ethambutol (EMB), or pyrazinamide (PZA)
• poly-resistance (other patterns) - resistance to two or more first-line drugs, not including the INH and RMP combination
• multidrug-resistant tuberculosis (MDR-TB) - TB that is resistant to at least the two best first-line anti-tuberculosis drugs, INH and RMP, but that does not meet the definition of extensively drug-resistant TB  (XDR-TB)
• extensively drug-resistant TB (XDR-TB) - TB that is resistant to at least the two best first-line anti-tuberculosis drugs, INH and RMP, and is 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

In Canada, the prevalence of drug-resistant TB remains low. Overall, from 2002 to 2012, of the 14,148 culture-positive cases tested for drug resistance, 1,049 (7.4%) were monoresistant to one of the first line drugs, 152 (1.1%) were MDR-TB, and six (0.04%) were classified as XDR-TB. An additional 68 cases were poly-resistant.

Of the 1,367 culture-positive cases reported in 2012, DST results were reported for 1,326 (97%). Approximately one in 10 of those with a DST result (n=130) were resistant to at least one of the four first-line medications (INH, RMP, EMB, and PZA), of which 120 (92%) were monoresistant. Of the 120 cases defined as monoresistant, 95 (79%) were resistant to INH, 23 (19%) were resistant to PZA, and two (2%) were resistant to EMB. No cases were resistant to RMP (Table 18-3).

Of the remaining 10 cases that were resistant to one or more anti-tuberculosis medications, eight cases had MDR-TB and one case had XDR-TB. The remaining case was defined as poly-resistant because the isolate showed resistance to both INH and PZA (Table 18-3). By comparison, 13 MDR-TB cases were reported in 2010 and 15 were reported in 2011. One XDR-TB case was reported in both 2010 and 2011 (Table 18-1 and Table 18-2). The eight MDR-TB cases reported in 2012 were resistant to INH and RMP, whereas, in addition to being resistant to INH and RMP, the XDR-TB case was resistant to KM, OFL, and MOX (Table 18-3).

In 2012, the majority (77%) of the 130 reported cases with resistance to one or more first-line anti-tuberculosis medications was foreign-born. An additional 15% were Canadian-born non-Aboriginal people and 7% were Canadian-born Aboriginal people.  All eight of the reported MDR-TB cases were foreign-born and the one XDR-TB case was a Canadian-born non-Aboriginal person (Table 18-3).

Case detection method

In 2012, 73% of reported TB cases were identified following investigation by a health care professional for signs and symptoms consistent with active TB disease (e.g. prolonged persistent cough, fever, lymphadenopathy, night sweats, and weight loss) (Table 19). The remaining cases were diagnosed using the following methods:

• 14% through a contact investigation
• 5% through immigration medical surveillance
• 3% through routine TB screening (school or occupational)
• 1%  other unspecified screening methods
• 0.6% post-mortem

Note: 3% had no case detection method reported

The case detection method varied by reporting province or territory. The percentage identified through contact investigation was highest in Nunavut at 54%, followed by Manitoba at 36% (Table 19). In Quebec, the percentage of cases detected through contact investigation increased from 5% in 2010 to 26% in 2012. This increase is partially attributable to TB outbreaks in northern regions of the province and contact investigations conducted as part of outbreak management. Overall, for Canada from 2002 to 2012, the percentage of reported cases found through contact investigations increased from 5% in 2002 to almost 14% in 2012.

With respect to origin, in 2012, 50% of Canadian-born Aboriginal cases (compared with 18% of Canadian-born non-Aboriginal cases and 2% of foreign-born cases) were identified through contact investigation. Immigration medical surveillance screening identified 7% of foreign-born cases (Table 20).

HIV status

The collection of data on the HIV status of individuals diagnosed with active TB disease was initiated in 1997, and there has been a slow but gradual increase in the percentage of cases for which HIV status is reported. The percentage of reported TB cases with data on HIV status has remained steady at approximately 40% since 2008 (Figure 16).

Figure 16: HIV status as a percentage of reported tuberculosis cases – Canada: 2002-2012

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In 2012, HIV status (positive or negative) was reported for 42% of all cases. Of the 715 reported TB cases with known HIV status, 8% were HIV-positive.

In 2012, HIV status was unknown (either no response was provided or was reported as “unknown”) for 50% of reported TB cases. An additional 4% of TB cases were reportedly not offered an HIV test, and for another 4%, an HIV test was reportedly offered but was refused by the individual.

The proportion of cases for which HIV status was reported varied across the provinces and territories, which may reflect differences in HIV testing practices. In 2012, HIV status was reported for 94% of TB cases in Alberta, 91% in the territories, 74% in British Columbia, and 61% in Quebec. For the remaining provinces, HIV status reporting ranged from 3% in Ontario to 55% in the Atlantic provinces (Table 21).