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November 3rd, 2009Lecture Notes Page 1 of 31 foundations of health science
TuberculosisGlobal and Local Epidemiology
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-$10 per patient / 6-8 months
-helps in the delivery of ARV treatment people with HIV/AIDS
-↓ incidence/prevalence of TB
-important to reduce drug resistant TB
DOTS
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Why is the treatment of TB difficult?-duration of treatment-asymptomatic early-regimen of pills
Why is the treatment of TB a critical piece in prevention?
What mechanisms are suggested to improve compliance with treatment regimen in global settings?
Treatment
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Drug Resistant TB
See the WHO TB WebsiteSee the Canadian Public Health Agency
Website
*handout in class
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www.stoptb.org
Visit this website for more information.
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Tuberculosis (TB disease) is a notifiable disease in all jurisdictions in Canada; health care providers must report all cases to Centres for Disease Control. In BC, BCCDC.
1965 : incidence rate – 29.0 cases per 100,000 (year)1995: incidence rate – 6.5 cases per 100,000 (year)2004: incidence rate - 4.9 cases per 100,000 (year)
There were 1574 cases of TB reported in Canada in 2004.
Epidemiology in Canada
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WHEREIncidence Rates 2004
.7 per 100,000 (PEI) 3 per 100,000 (Quebec) 5 per 100,000 (Ontario) 12 per 100,000 (Manitoba) 7 per 100,000 (BC)108 per 100,000 (Nunavut)
MOST cases in Ont, BC, QueOntario = 42% of casesBC = 19% of cases
13.8 per 100,000 (Toronto)
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WHERE?Incidence Rates 2004
Risk Settings In Toronto
Risk Setting
Number of Cases
%
Travel / Living in Endemic Area
311 90%
Home 15 4%
Shelter 15 4%
Work 2 <1%
Residence
1 <1%
Hospital 1 <1%
Other 1 <1%
Total 346
Unknown 12
Overall 358
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WHERE?British Columbia &
Vancouver Downtown Eastside
BC – 2001391 cases9.5 per 100,000
Downtown Eastside85.1 per 100,000 (2001)
28.9 per 100,000 (2004) after TB program
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WHO? Incidence Rates 2004Ethnicity/Place of Birth17% cases Aboriginal13% cases Canadian born68% cases Foreign born2% cases unknown birthplace
267/464 cases among people born in Canada – cases in Aboriginal population (58%)
Fitzgerald Reading: rates in Aboriginals vary by geography-105 cases per 100,000 (Sask) to no cases in Atlantic
Canada -1996: incidence rate 18 times higher in Aboriginal vs. Canadian born non-Aboriginal descent
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WHO?Incidence Rates 2004
Age
Who is most affected?
Gender
Age Group Incidence per 100,000
<1 years 1.8
1-4 years 2.4
5-14 years 1.1
15-24 years 4.5
25-34 years 7.1
35-44 years 5.2
45-54 years 4.1
55-64 years 4.9
65-74 years 7.5
75 + years 9.8
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Types of prevention:1. Prevent new cases of infection2. Prevent activation and reactivation of disease
• Vaccination • Diagnosis and Treatment play critical roles in
PREVENTION of TB
Case finding: attempts at early detection of cases
Prevention of Tuberculosis
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1921, Albert Calmette and Camille Guerin create BCG 1924 France begins vaccination of children
• BCG part of standard vaccines in WHO Expanded Programme on Immunization, implemented in 100 countries
• Administered at birth
Efficacy?
-Canada? -BCG contraindicated if HIV infection is present
BCG Vaccination
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Accuracy of Testing
Measuring accuracy – do the test results correspond to the true state of the phenomenon?
Sensitive tests – ideal case – your test will identify all people with disease (most people with disease identified)
Specific tests – ideal case – your test will identify only people with disease (most identified actually have disease)
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Sensitivity and SpecificitySensitivity – how well does the
test classify people with disease as diseased?
True positives X 100Number with disease Diagram: A / A + CDecreasing false negatives will
increase proportion of true positives
Specificity – how well does the test classify people without disease as non-diseased?
True negatives X 100Number without diseaseDiagram: D/ B + DDecreasing false positives will
increase proportion of true negatives
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Sensitivity and Specificity ExampleSensitivity – True positives X 100Number with disease example: 75 / 75+ 25 = 75%
Specificity –
True negatives X 100
Number without diseaseexample: 95/ 5 + 95 = 95%
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Improving Diagnostics for TB
Increasing the sensitivity of TB tests-decrease number of false negativesQ: why is this important to TB prevention?
Improving the specificity of TB tests-decrease the number of false positivesQ: why is this important to TB prevention?
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TB Skin Test-errors in technique can lead to false positive and false
negative-Canada – TB test positive if reaction > 10 mm therefore
further diagnostics
Anergy - (non-responsiveness of immune system)
Tests
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Factors that influence false positives:
1. non-tuberculosis mycobacteria (tropical/subtropical climates e.g. Southern US)
2. BCG vaccination
-received before 2 years of age – not likely to be the case-received in childhood/adolescence – 15%-25% have positive
reactions up to 20 years later
Tests
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Factors that influence false negatives:
• Immunosupression: HIV patients – 20% with CD4>500 and 80-100% with CD4<200
• malnutrition• corticosteroid use• concurrent viral illness• Recent TB infection (2-10 weeks for reaction)• Very young age (immune system not developed)
Tests
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Preventing Transmission: Recommended Guidelines
1. Suspected cases in respiratory isolation; ideally in hospital
2. Quasi-isolation at home [ no work, school, indoor public places]
3. No contact with people susceptible to TB
4. Compliance with therapy
Q: What are the challenges in Canada?
Prevention