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INFECTIOUS DISEASE SURVEILLANCE
in Canadian Federal Penitentiaries 2005-2006

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Part II: Results

Chapter 6: Tuberculosis Screening among Inmates

Participation in Assessment

Inmate participation in tuberculosis (TB) screening from 1998 – 2006 is shown in Table 6.1. Among inmates participation in TB assessment was 81.8% in 2005 and 79.5% in 2006.

Initial Assessment - Inmates

The results of the initial assessment for inmates 2005 – 2006 by region are shown in Appendix E, Table E.1. Overall, the proportion that tested positive for tuberculosis infection on initial assessment was 11.6% in 2005 and 13.3% in 2006. Figure 6.1 indicates a general decrease in the proportion positive for LTBI on initial assessment since a high of 21.3% in 1998, with a slight rise in 2006. The proportion invalid (see Introduction and Methods section) was 8.6% in 2005 and 13.6% in 2006. The proportion of assessments where the TST was refused was 3.2% in 2005 and 2.7% in 2006.

Table E.1, Appendix E, shows that in both 2005 and 2006 the proportion of inmates who tested positive on their initial assessment was highest in the Quebec Region (23.5% in 2005, 27.3% in 2006). The lowest proportion testing positive was in the Pacific Region in 2005 (5.0%) and the Atlantic Region in 2006 (4.5%). The proportion of records that were deemed invalid was highest in the Prairie Region in both 2005 (14.8%) and 2006 (17.3%), and lowest in Ontario for 2005 (4.5%) and Pacific for 2006 (8.7%). The proportion of refusals was highest in Quebec Region in both 2005 (8.1%) and 2006 (9.2%).

BCG Vaccination Status - Inmates

As part of the Initial Assessment, a TB medical history is taken that includes a history of Bacille Calmette-Guérin (BCG) vaccination. The proportion of inmates reporting a history of BCG vaccination by region and origin is shown in Appendix E, Table E.2. The overall proportion of inmates with a BCG history was 11.6% in 2005 and 9.9% in 2006. Apart from the origin unknown category, the highest proportion with BCG was observed among the Foreign-born for both 2005 (15.0%) and 2006 (16.2%), while the lowest proportion reporting a BCG history was among Aboriginals in both 2005 (11.1%) and 2006 (8.0%).

Regionally, Quebec had the highest overall proportion reporting a BCG history for both 2005 and 2006 (29.0% and 24.9% respectively). Atlantic Region had the lowest proportion of inmates reporting a history of BCG in 2005 (1.4%), and Pacific Region had the lowest proportion in 2006 (2.7%).

BCG history and age at vaccination by origin and TST status on initial assessment for 39,022 inmates (1998-2006) are shown in Table 6.2. Overall, a total of 13.4% of inmates reported a history of BCG vaccination. A higher proportion of Foreign-born (18.1%) and Canadian-born Aboriginal (15.0%) inmates reported a history of BCG compared to Canadian-born non-Aboriginal inmates (11.5%). Age at vaccination was available for 59.5% of inmates reporting a BCG history (data availability varied by origin). These data indicate that Canadian-born Aboriginal inmates report a lower mean age at vaccination, roughly half that of other origin categories; in fact, half of all Aboriginal inmates who reported a BCG history were vaccinated between birth and age 5 years.

Among inmates with a positive result on initial assessment, 24.8% had a history of BCG compared to 10.9% of those with a negative TST result and 14.0% of those with an ‘other’ result. Age at vaccination did not vary by TST status at admission.

 

Table 6.1: Participation1 in TB Assessment, Inmates, 1998-2006
  1998 1999 2000 2001 2002 2003 2004 2005 2006

1 – Participation rate calculated by adding annual new admissions to the inmate population as
of January 1st of that year.
Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

Inmates 12,413 (86.2%) 13,399 (77.4%) 13,013 (78.1%) 13,197 (78.7%) 13,223 (80.4%) 13,460 (82.0%) 13,470 (76.9%) 13,938 (81.8%) 14,588 (79.5%)

 

Figure 6.1: Initial TB Assessment Results, Inmates, 1998-2006 FFigure 6.1: Initial TB Assessment Results, Inmates, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Ongoing Negative Assessment - Inmates

The results of the ongoing screening of inmates with a previous negative TST for 1998 – 2006 are shown in Figure 6.2 (see also Appendix E, Table E.3). The proportion of inmates testing positive on a follow up TST was 1.5% in 2005 and 1.5% in 2006. The overall proportion of invalid records was 3.6% in 2005 and 3.2% in 2006. The proportion that refused the TST on follow-up assessment was 7.2% in 2005 and 6.6% in 2006.

Appendix E, Table E.3 shows that the highest proportion testing positive on an ongoing assessment in both 2005 and 2006 was in Prairies Region (2.5% and 2.4% respectively). The lowest proportion was in Quebec in 2005 (0.8%), and in Atlantic and Ontario in 2006 (both 0.7%). The highest proportion of invalid records in both 2005 and 2006 were from the Pacific Region (7.7% and 8.7% respectively), while the lowest was in Ontario in both 2005 and 2006 (2.5% and 1.6% respectively). Quebec Region had the highest proportion of refusals in both 2005 and 2006 (16.8% and 16.0% respectively) while the lowest proportion of refusals was in Ontario in both 2005 and 2006 (3.1% and 2.8% respectively).

Tuberculin Skin Test (TST) Converters and Conversion Rate - Inmates

Analysis of the previous TST history for inmates who tested positive on an ongoing negative assessment allows the estimation of the conversion rate. A converter is defined as a person with a previously documented negative TST result who now has a positive TST result. Table 6.3 shows the number of inmates with a newly positive TST, and of those, the number with a previous documented negative assessment (“true” converters). Note that the number of years between assessments for each inmate in this proportion varies depending on how long ago a valid negative record was recorded. The fourth line in the table shows the number of inmates with a previous valid result of those who had an assessment in that year (line 1), (i.e., the total number “at risk” of converting that year). Finally, dividing the true converters by those “at risk” of conversion provides an estimated conversion rate for that year.

These data show that the estimated TST conversion rate among inmates was 0.90% in 2005 and 0.89% in 2006.

 

Table 6.2: BCG Vaccination and Age at Vaccination at Initial Assessment, Inmates, 1998-2006
Category Number Number (%) BCG History Number (%) with Information on Age at Vaccination Mean (Median) Age in years at Vaccination

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010
1 – Other includes: blank/missing, refused, invalid, contraindicated.

Ethnic/Country of Origin
Canadian-born
non-Aboriginal
19,271 2,210 (11.5%) 1,514 (68.5%) 9.5 (7)
Canadian-born Aboriginal 6,863 1,029 (15.0%) 468 (45.5%) 5.5 (3)
Foreign-born 3,543 641 (18.1%) 316 (49.3%) 11.4 (8.5)
Unknown 9,345 1,346 (14.4%) 810 (60.2%) 9.5 (7)
TST Status
Positive 5,235 1,300 (24.8%) 793 (61.0%) 9.1 (7)
Negative 26,007 2,835 (10.9%) 1,682 (59.3%) 8.8 (7)
Other1 7,780 1,091 (14.0%) 633 (58.0%) 10 (7)
TOTALS 39,022 5,226 (13.4%) 3,108 (59.5%) 9.1 (7)

 

Figure 6.2: Ongoing Negative TB Assessment Results, Inmates, 1998-2006Figure 6.2: Ongoing Negative TB Assessment Results, Inmates, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Table 6.3: Newly Positive TST, Converters, and Conversion Rate, Inmates, 2000-2006
  2000 2001 2002 2003 2004 2005 2006
Source: Web-IDSS Enhanced Surveillance Data, CSC 2010
Number of Ongoing Negative Assessments 7,254 7,484 7,662 7,689 7,878 8,179 9,017
Number Newly Positive on Ongoing Assessment 88 159 124 115 91 98 107
Number with a Previous Valid Negative Result 41 85 73 66 45 51 54
Total Number with a Valid Previous Result 5,158 5,182 5,029 5,402 5,430 5,674 6,041
Estimated Conversion Rate 0.79% 1.64% 1.45% 1.22% 0.83% 0.90% 0.89%

 

TST Conversion Rates by Origin

Using the approach for estimating TST conversion and stratifying the data by origin, it is possible to examine TST conversion by origin for 2000 – 2006 (see Figure 6.3). Apart from the observation that the conversion rate for Foreign-born individuals tends to be highest, and the rate for Canadian-born Non-Aboriginals is lowest, the data are too limited to draw many conclusions.

Ongoing Positive Assessments14 - Inmates

The number of assessments for inmates known to have had a previous positive TST (and therefore assumed to be latently infected with tuberculosis after active disease has been ruled out) by year and region is shown in Table 6.4. The number of ongoing positive assessments reported was 1,643 in 2005 and 1,820 in 2006.

 

Figure 6.3: TST Conversion Rate by Origin, Inmates, 2000-2006 Figure 6.3: TST Conversion Rate by Origin, Inmates, 2000-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Table 6.4: Ongoing Positive Assessments by Region, Inmates, 1998-2006
  1998 1999 2000 2001 2002 2003 2004 2005 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010
1 – includes region "Unknown" (2005:N=30; 2006:N=34)

Atlantic 89 126 95 90 83 76 89 74 66
Quebec 365 603 438 637 583 582 494 458 576
Ontario 659 758 584 467 368 379 428 430 507
Prairies 461 509 611 536 511 571 553 513 506
Pacific 114 134 153 207 232 204 182 138 131
Canada1 1,691 2,130 1,882 1,937 1,783 1,837 1,778 1,643 1,820

 

Figure 6.4: Latent Tuberculosis Infection (LTBI) by Region, Inmates, 1998 - 2006 Figure 6.4: Latent Tuberculosis Infection (LTBI) by Region, Inmates, 1998 - 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Latent Tuberculosis Infection - Inmates

The overall proportion of inmates considered to be infected with Mycobacterium tuberculosis is calculated by adding the number of inmates with a newly positive TST (either on their initial assessment, on a follow up assessment) in a year with those already considered to have latent tuberculosis infection (LTBI) (includes ongoing positive assessments and those previous positive on initial assessment). The regional distributions of LTBI by age, origin, and gender for 2005 – 2006 are shown in Appendix E (Table E.4, E.5, and E.6 respectively).

Figure 6.4 shows the estimated proportion of inmates assumed to have LTBI by region for 1998 – 2006. The overall proportion of inmates considered to have LTBI has been decreasing over time and was 15.8% in 2005 and 16.6% in 2006. The region with the highest proportion of inmates having LTBI was Quebec for both 2005 (21.2%) and 2006 (23.9%). The region with the lowest proportion having LTBI was Atlantic for both 2005 (8.3%) and 2006 (7.3%).

LTBI by Age Category

The proportion of inmates who are assumed to have LTBI increases with age (Appendix E, Table E.4). For example, in 2006, the proportion LTBI was 10.5%, 9.7%, 14.8%, 21.2%, 30.0%, and 29.6% respectively for ages 17-19, 20-29, 30-39, 40-49, 50-59, and 60 plus years.

LTBI by Origin

Figure 6.5 shows the proportion of inmates having LTBI by origin from 1998-200615. Apart from the unknown category, Canadian-born non-Aboriginals consistently had a lower proportion LTBI compared to Foreign-born and Canadian-born Aboriginals. Foreign-born inmates had the highest proportion of LTBI in every year. Among Foreign-born inmates, the rate was 35.6% in 2005 and 42.5% in 2006. Among Canadian-born Aboriginal inmates the proportion with LTBI was 21.2% in 2005 and 20.0% in 2006. Among Canadian-born non-Aboriginals, the LTBI rate was 9.6% in 2005 and 10.7% in 2006.

Analysis of Appendix E, Table E.5 reveals regional differences. Among the Foreign-born, the highest rates were observed in Prairie Region in 2005 (45.4%) and in Quebec Region in 2006 (49.5%). Among Canadian-born Aboriginals, the highest proportions were observed in Prairie Region in both 2005 (24.1%) and 2006 (23.2%). Among Canadian born non-Aboriginals, the highest rates were reported among inmates in the Quebec Region in 2005 (16.6%) and 2006 (19.3%).

 

Figure 6.5: Latent Tuberculosis Infection (LTBI) by Origin, Inmates, 1998 - 2006 Figure 6.5: Latent Tuberculosis Infection (LTBI) by Origin, Inmates, 1998 - 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

LTBI by Gender

Figure 6.6 shows the proportion LTBI by gender for 1998-2006. Among males, the proportion having LTBI was 16.1% in 2005 and 16.8% in 2006. Among females, the proportion having LTBI was 8.4% in 2005 and 11.3% in 2006.

Inspection of Appendix E, Table E.6 indicates regional differences between LTBI rates among genders. The highest proportion LTBI among males were observed in the Quebec Region for both 2005 (21.6%) and 2006 (24.4%). Among women, the highest proportion having LTBI were observed in Prairie Region in both 2005 (11.7%) and 2006 (12.7%).

 

Figure 6.6: Latent Tuberculosis Infection (LTBI) by Gender, Inmates 1998 - 2006 Figure 6.6: Latent Tuberculosis Infection (LTBI) by Gender, Inmates 1998 - 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Symptoms and Risk Factor Screening - Inmates

The results of the screening checklist for risk factors and symptoms for 2005-2006 are shown in Tables E7.i and E7.ii, respectively. Symptom screening is a crucial part of the tuberculosis assessment to rule out active TB disease. Risk factors included in the screening process are those that are risks for progression to active TB, and are not necessarily risk factors for acquiring tuberculosis infection.

Symptoms

Overall, the most frequently reported symptoms in 2005 were fatigue (6.23%), chest pains (4.73%), productive cough (3.72%), night sweats (3.62%), and loss of appetite (3.24%). The same symptom rank-order was observed when only those with a positive TST are considered (fatigue: 8.28%; chest pains: 6.64%; productive cough: 6.28%; night sweats: 4.96%; and loss of appetite: 4.64%). Among those with a negative or other (invalid, refused, blank/unknown) TST result in 2005, virtually the same rank-order was observed (fatigue: 5.86%; chest pains: 4.39%; night sweats: 3.38%; productive cough: 3.25%; and loss of appetite: 2.99%).

The same rank-order was observed for the most frequently reported symptoms overall in 2006. They were: fatigue (4.90%), chest pains (4.08%), productive cough (3.37%), night sweats (3.32%), and loss of appetite (3.25%). Similarly, among those with a positive TST in 2006, the most common symptoms were fatigue (5.99%), chest pains (5.20%), productive cough (4.92%), loss of appetite (4.50%) and night sweats (3.97%). Among those with a negative or other (invalid, refused, blank/unknown) TST result in 2006, virtually the same rank-order was observed (fatigue: 4.69%; chest pains: 3.87%; night sweats: 3.20%; productive cough: 3.08%; and weight loss: 3.05%).

Risk Factors

Overall, the most frequently reported risk factors for progression to active tuberculosis disease in 2005 were a history of injection drug use (11.68%), diabetes (2.24%), steroid use (1.67%), previous contact with an active TB case (1.58%), and HIV/AIDS (1.45%). Among those with a positive TST in 2005, the most frequently reported risk factors were a history of injection drug use (9.28%), diabetes (3.59%), previous contact with an active TB case (2.64%), steroid use (0.96%), and HIV/AIDS (0.86%). This pattern is similar for those with a negative or other (invalid, refused, blank/unknown), where the most common reported risk factor in 2005 was injection drug use (12.12%), diabetes (2.00%), steroid use (1.80%), HIV/AIDS (1.56%), and previous contact with an active TB case (1.39%).

Overall, the most frequently reported risk factors for progression to active tuberculosis disease in 2006 were a history of injection drug use (13.05%), diabetes (3.29%), previous contact with an active TB case (3.12%), steroid use (1.96%), and HIV/AIDS (1.45%). The pattern is the same among those with a positive TST in 2006. The most frequently reported risk factors were a history of injection drug use (11.03%), diabetes (5.04%), previous contact with an active TB case (4.01%), steroid use (1.07%), and HIV/AIDS (0.99%). Again, this pattern is repeated for those with a negative or other (invalid, refused, blank/unknown) test, where the most common reported risk factors in 2006 were injection drug use (13.43%), diabetes (2.96%), previous contact with an active TB case (2.95%), steroid use (2.12%), and HIV/AIDS (1.54%).

LTBI Treatment - Inmates

The number of inmates on LTBI treatment is submitted via the CSC IDSS system (see Appendix E, Table E.8). Each institution reports the number of inmates on prophylactic LTBI therapy16 in a given month. Thus it is possible to calculate the average number of inmates on LTBI therapy per month by region, and by aggregating across regions, for CSC overall.

Table 6.5 shows the number of inmates with LTBI and the average monthly number of inmates on prophylactic therapy for LTBI for 1999 to 2006. The total number of inmates with LTBI has trended downwards from 2,946 in 1999 to 2,421 in 2006 while the number of inmates on LTBI therapy per month has trended up from 44 in 1999 to 103 in 2006.

 

Table 6.5: Average Monthly Number of Inmates on Prophylactic Therapy for LTBI, 1999 – 2006
  1999 2000 2001 2002 2003 2004 2005 2006

Source: IDSS Aggregate Surveillance Data, CSC 2010

Number of inmates with LTBI 2,946 2,654 2,760 2,494 2,532 2,259 2,198 2,421
Average number on LTBI therapy per month 44 57 72 64 49 84 99 103

 

Appendix E, Table E.8 shows the total number of inmates with LTBI and the average monthly number of inmates on LTBI therapy by region for 2005 – 2006. Ontario reported the highest average number of inmates on LTBI treatment per month in both 2005 (53) and 2006 (50).

Active TB Disease among Inmates

Cases of active tuberculosis disease (Active TB) are reported via the CSC IDSS. The number of active TB cases diagnosed and reported among inmates in CSC was 7 in 2005 and 3 in 2006 (Figure 6.7). These case reports translate into yearly case rates per 100,000 of 41.1, and 16.3 respectively.

 

Figure 6.7: Active TB Case Frequency and Rate, Inmates, 1998 - 2006 Figure 6.7: Active TB Case Frequency and Rate, Inmates, 1998 - 2006

Source: IDSS Aggregate Surveillance Data, CSC 2010

* - Case Rate: rate per 100,000; ** - % LTBI: Proportion having LTBI (percent)

 

Figure 6.8: Active TB Disease in CSC versus Active TB Disease
in Canada by Origin, 1998 – 2006
Figure 6.7: Active TB Case Frequency and Rate, Inmates, 1998 - 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010 and Tuberculosis in Canada 2007, Public Health Agency of Canada, Minister of Public Works and Government Services Canada, 2009

 

Since the absolute number of active TB cases is small, a centred 3-year moving average was calculated (see Figure 6.7). This operation has the effect of smoothing the highs and lows in the solid black line depicting the annual CSC active TB case rate. The centred 3-year moving average was 23.6 / 100,000 in 2004 and 22.9 / 100,000 in 2005.

The active TB case rate in CSC is generally higher than in the Canadian population. In 2005 and 2006 the TB case rate in Canada was 5.1 per 100,000 (PHAC, 2009). Figure 6.8 shows the active TB rate in CSC (red) and the rates in the Canadian population by origin. In Canada, the highest rates are observed among Canadian-born Aboriginal and Foreign-born Canadians, at 27.4 and 14.8 per 100,000 in 2006. Among Canadian-born non-Aboriginals, the rate was 0.8 per 100,000 in 2006. The variability in the CSC rate is highlighted when juxtaposed against these other data.


Footnote

14 The ongoing positive tuberculosis assessment does not include a tuberculin skin test; rather, the assessment is conducted to ensure that the patient has not progressed to active disease, based on a symptom screen and a chest x-ray. The risk of progression to active disease is highest in the two years following TST conversion.

15 Considerable efforts to improve data quality have been undertaken since the publication of the last report in 2008; reassigning the unknown to their respective true categories has resulted in an adjustment to the LTBI rate estimates in this report. The estimates presented here are believed to be a more precise estimate given the improvements in data quality.

16 LTBI treatment usually consists of 9 months isoniazid regimen. However, the course of treatment for each individual is determined by the institutional physician and may vary accordingly (CSC, 2004).

 

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