lecture 12 - tuberculosis part ii - nov 3 2009

November 3rd, 2009Lecture Notes of 31 foundations of health science

TuberculosisGlobal and Local Epidemiology

November 3rd, 2009Lecture Notes of 31

foundations of health science

-$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



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



Drug Resistant TB

See the WHO TB WebsiteSee the Canadian Public Health Agency

Website

*handout in class



www.stoptb.org

Visit this website for more information.



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



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)



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



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



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



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



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



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



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)



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



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%



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?



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



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



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



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

lecture 12 - tuberculosis part ii - nov 3 2009

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