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INFECTIOUS DISEASE SURVEILLANCE
in Canadian Federal Penitentiaries 2005-2006

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Part II: Results

Chapter 7: Tuberculosis Screening among Staff

Participation in TB Assessment

Participation in tuberculosis assessment for CSC staff, which includes every CSC employed individual, from 1998 – 2006 is shown in Table 7.1. Among staff, the participation rate was 12.4% in 2005 and 17.9% in 2006.

 

Table 7.1: Participation in TB Assessment, Staff, 1998-2006
  1998 1999 2000 2001 2002 2003 2004 2005 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

Staff 4,319 (38.6%) 3,986 (28.2%) 3,327 (20.6%) 3,299 (19.8%) 2,969 (17.2%) 3,278 (19.6%) 2,376 (14.0%) 1,995 (12.4%) 2,939 (17.9%)

 

Initial Assessment - Staff

The results of the initial assessment for staff for 2005 – 2006 by region are shown in Figure 7.1 and Appendix F, Table F.1. Overall, the proportion that tested positive for tuberculosis infection on initial assessment was 8.2% in 2005 and 5.7% in 2006. The proportion of invalid assessments (see Methods section) reached a high of 34.9% in 2003, but declined to 25.9% in 2005 and 17.8% in 2006. The proportion of assessments where the TST was refused was 0.2% in 2005 and 0.3% in 2006, and has been below 1.0% since 2001.

 

Figure 7.1: Initial TB Assessment Results, Staff, 1998-2006 Figure 7.1: Initial TB Assessment Results, Staff, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Appendix F, Table F.1 shows that the regions with the highest proportions of staff who were positive on initial assessment in 2005 were Quebec (22.5%) and Prairies (13.2%). In 2006 the regions with the highest proportion positive were Quebec (19.2%) and Atlantic (6.9%). Pacific Region had the lowest proportions of positive results in both 2005 (0.0%) and 2006 (2.9%). Regionally, the proportion of tests that were invalid was highest in Pacific in 2005 (72.2%) and 2006 (37.5%). The overall proportion of assessments that were refused was 0.0% for 2005-2006 for Atlantic, Ontario, Prairies, and Pacific; Quebec reported one refusal in 2005 (1.7%) and none in 2006.

BCG Vaccination Status - Staff

The proportion of staff reporting a history of BCG vaccination on initial assessment, by region and origin, is shown in Appendix F, Table F.2. The overall proportion of staff reporting a BCG history was 8.4% in 2005 and 8.0% in 2006. Apart from the origin unknown category, the highest proportion with BCG was observed among the Foreign-born for 2005 (11.1%) and 2006 (22.2%). BCG vaccination was least common among Canadian-born non-Aboriginal staff in 2005 (6.4%) and 2006 (6.9%).

 

Table 7.2: BCG Vaccination and Age at Vaccination at Initial Assessment, Staff, 1998-2006
Category Number Number (%) BCG History Number (%) with Age at Vaccination Mean (Median) Age at Vaccination

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

Origin
Canadian 4,788 838 (17.5%) 700 (83.5%) 10.4 (8)
Aboriginal 492  59 (12.0%)  32 (54.2%) 11.5 (9)
Foreign-born 374  65 (17.4%)  40 (61.5%) 13.9 (9)
Unknown 1,434 206 (14.4%) 140 (68.0%) 12.2 (9)
TST Status
Positive 372 168 (45.2%) 137 (81.5%) 9.8 (9)
Negative 4,141 646 (15.6%) 530 (82.0%) 10.5 (8)
Other1 2,574 354 (13.8%) 245 (69.2%) 12.3 (9)
TOTALS 7,088 1,168 (16.5%) 912 (78.1%) 10.9 (9)

 

Regionally, Quebec had the highest overall proportion of staff with a BCG history (33.9% in 2005 and 24.1% in 2006). Prairie Regions had the lowest proportions of staff reporting a history of BCG (1.6% in 2005 and 3.1% in 2006).

BCG history and age at vaccination, by origin and TST status, on initial assessment for 7,088 CSC staff, from 1998-2006, are shown in Table 7.2. Overall, 16.5% of staff reported a history of BCG vaccination. Canadian-born Aboriginal staff reported a lower proportion of vaccination (12.0%) than Canadian-born non-Aboriginal (17.5%) or Foreign-born (17.4%) staff.

Age at vaccination was available for 78.1% of staff reporting a BCG history. Data availability varied by origin (Canadian-born non-Aboriginal [83.5%], Foreign-born [61.5%], and Canadian-born Aboriginal [54.2%]). The data indicate that among staff, mean age at vaccination was 13.9 yrs among Foreign–born, 11.5 yrs among Canadian-born Aboriginal and 10.4 yrs among Canadian-born non-Aboriginal staff. Mean age at BCG vaccination was lower among those with a positive (9.8 yrs) or negative (10.5 yrs) TST result compared to those with an ‘other’ test result (12.3 yrs). Among staff with a positive TST result on an initial assessment, 45.2% reported a history of BCG, compared to 15.6% of those with a negative TST.

Ongoing Negative Assessment - Staff

The results of the ongoing screening of staff with a previous negative TST for 1998-2006 are shown in Figure 7.2 (see also Appendix F, Table F.3). Overall, the proportion of staff testing positive on a follow-up TST was 1.6% in 2005 and 1.7% in 2006. The proportion of invalid records was 19.2% in 2005 and 11.1% in 2006. The proportion refusing a TST at follow-up assessment was 0.4% in 2005 and 0.1% in 2006.

 

Figure 7.2: Ongoing Negative TB Assessment Results, Staff, 1998-2006 Figure 7.2: Ongoing Negative TB Assessment Results, Staff, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Regionally, the highest proportion of positive TST results (Appendix F, Table F.3) was reported in Quebec for 2005-2006 (8.2% and 7.7% respectively). The highest proportions of invalid records were found in the Pacific Region in 2005 (53.0%) and 2006 (56.3%). In 2005, there were zero refusals in Ontario and Quebec, one refusal in both the Pacific Region (0.3%) and Prairie Region (0.7%), and Regions, and 4 refusals in Atlantic Region (0.9%). In 2006, there was one refusal in Prairie Region (0.1%). There were zero refusals in all other regions.

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

Analysis of the previous TST history for staff 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 7.3 shows, for 2000 – 2006, the number of staff with a newly positive TST, and of those, the number with a previous documented negative assessment (“true” converters). The fourth line in the table shows the number of staff 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 number of new positives with a previous valid negative result, by the number of individuals “at risk” of conversion provides an estimated conversion rate for that year.

These data show that the estimated TST conversion rate among staff was 0.82% in 2005 and 0.66% in 2006.

Ongoing Positive Assessments - Staff

The number of assessments for staff known to have had a previous positive TST (and therefore assumed to be latently infected with tuberculosis) by year and region are shown in Table 7.4. The number of ongoing positive assessments reported to NHQ was 79 in 2005 and 107 in 2006.

 

Table 7.3: Newly Positive TST, Converters, and Conversion Rate, Staff, 2000-2006
  2000 2001 2002 2003 2004 2005 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

Number of Ongoing Negative Assessments 2,131 2,326 1,806 2,539 1,611 1,514 2,181
Number Newly Positive on Ongoing Assessment 8 7 22 16 13 19 31
Number Newly Positive with a Previous Valid Negative Result 3 3 3 7 7 8 10
Total Number with a Valid Previous Result 1,329 1,412 1,054 1,532 1,012 980 1,506
Estimated Conversion Rate 0.23% 0.21% 0.28% 0.46% 0.69% 0.82% 0.66%

 

Table 7.4: Ongoing Positive TST by Region, Staff, 1998-2006
  1998 1999 2000 2001 2002 2003 2004 2005 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

Atlantic 26 20 17 17 17 16 17 15 17
Quebec 0 1 0 0 0 0 1 2 0
Ontario 106 88 37 24 6 1 6 10 9
Prairies 203 170 173 84 117 82 94 32 64
Pacific 81 94 77 69 39 54 21 13 5
Unknown 3 0 3 3 12 16 15 7 12
Canada 419 373 307 197 191 169 154 79 107

 

Figure 7.3: Latent Tuberculosis Infection (LTBI) by Region, Staff, 1998-2006 Figure 7.3: Latent Tuberculosis Infection (LTBI) by Region, Staff, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Latent Tuberculosis Infection - Staff

The overall proportion of staff considered to be infected with Mycobacterium tuberculosis is calculated by adding the number of staff with a newly positive TST (either on their initial assessment, or 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 F (Tables F.4, F.5, and F.6 respectively).

Figure 7.3 shows the estimated proportion of staff assumed to have LTBI by region for 1998 – 2006. The overall proportion of staff considered to have LTBI was 6.6% in both 2005 and 2006. The region with the highest proportion of staff having LTBI was Prairies in 2005 (15.9%) and Quebec in 2006 (11.1%). Ontario had the lowest proportions of staff with LTBI in 2005 (3.7%) and 2006 (3.6%).

LTBI by Age Category

The proportion of staff who are assumed to have LTBI increases with age (Appendix F, Table F.4). For example, in 2006, the proportion LTBI was 0.0%, 3.6%, 4.3%, 8.2%, 9.0% and 12.8% respectively for ages 17-19, 20-29, 30-39, 40-49, 50-59, and 60 plus years.

LTBI by Origin

Figure 7.4 shows the proportion of staff with LTBI by origin for 1998-2006. Canadian-born non-Aboriginals had a lower proportion LTBI than Foreign-born or Canadian-born Aboriginal staff in all years except 2001. The highest proportions of LTBI were consistently found among the Foreign-born (22.2% in 2005 and 16.1% in 2006). Among Aboriginals, the proportion having LTBI was 7.7% in 2005 and 9.2% in 2006. Analysis of Appendix F, Table F.5 reveals differences in proportions across regions.

LTBI by Gender

Figure 7.5 shows the proportion of LTBI by gender for staff 1998-2006. Among males, the proportion with LTBI was 6.9% in 2005 and 6.4% in 2006. Among females, the proportion having LTBI was 6.3% in 2005 and 6.5% in 2006. Inspection of Appendix F, Table F.6 indicates regional differences between LTBI rates among genders for staff.

 

Figure 7.4: Latent Tuberculosis Infection (LTBI) by Origin, Staff, 1998-2006 Figure 7.4: Latent Tuberculosis Infection (LTBI) by Origin, Staff, 1998-2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

Risk Factor and Symptoms Screening - Staff

The results of the staff checklist screening for TB symptoms and risk factors for 2005-2006 are shown in Appendix F, Tables F.7.i and F.7.ii. Symptom screening is a crucial part of the tuberculosis assessment to rule out active TB disease. Risk factors included in the screen are those that are risks for progression to active TB disease, and are not necessarily risk factors for acquiring tuberculosis infection.

Symptoms

Overall, the symptoms most frequently reported by staff in 2005 were productive cough (2.45%), fatigue (1.40%) and hoarseness (1.35%). Among staff with a negative TST, productive cough (2.46%) was the most common symptom, followed by chest pains (1.23%) and hoarseness (1.23%). Among staff with a positive TST, the most common symptoms were fatigue (4.58%), night sweats (3.82%) and hoarseness (3.05%).

The most frequently reported symptoms, overall, in 2006 were fatigue (1.97%), productive cough (1.93%) and night sweats (1.32%). This same rank order was observed among staff with a negative TST [fatigue (1.85%), productive cough (1.78%) and night sweats (1.23%)]. Staff with positive TSTs most frequently reported productive cough (4.15%), fatigue (3.63%), chest pains (3.11%) and hoarseness (3.11%).

Risk Factors

Overall, the risk factor most frequently reported by staff in 2005 was contact with an active TB case (2.85%). This was followed closely by diabetes (2.80%) and then by oral steroid use at 1.40%. Diabetes was the most common risk factor among TST-negative staff (2.78%), followed by contact with an active TB case (2.73%) and oral steroid use (1.28%). TST positive staff reported contact with an active TB case (4.58%), diabetes (3.05%) and oral steroid use (3.05%) most frequently.

The most frequently reported risk factor in 2006 overall was contact with an active TB case (7.66%), followed by diabetes (2.85%) and oral steroid use (1.46%). These risk factors were those most reported by staff with a negative TST: contact with an active TB case (7.72%), diabetes (2.94%), oral steroids (1.41%). For staff with a positive TST, the most frequently reported risk factors were contact with an active TB case (6.74%) and oral steroid use (2.07%).

 

Figure 7.5: Latent TB Infection by Gender, Staff, 1998 - 2006 Figure 7.5: Latent TB Infection by Gender, Staff, 1998 - 2006

Source: Web-IDSS Enhanced Surveillance Data, CSC 2010

 

 

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