lecture 12 - tuberculosis part ii - nov 3 2009

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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