Epidemiology of Tuberculosis

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Epidemiology of Tuberculosis

• Ashry Gad Mohamed
• Prof. of Epidemiology
• College of Medicine, KSU

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Magnitude of the problem

• Annually 8 million new cases
• 3 million deaths
• 95 from developing countries
• 19-43 of world population is infected
• Between 2000-2020 G.
• One billion will get infection
• 200 million get sick
• 35 million will die

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WHO REPORT 2007 GLOBAL TUBERCULOSIS CONTROL

• TB is still a major cause of death worldwide, but
  the global epidemic is on the threshold of
  decline
• 1. There were an estimated 8.8 million new TB
  cases
• in 2005, 7.4 million in Asia and sub-Saharan
  Africa.
• A total of 1.6 million people died of TB,
  including
• 195 000 patients infected with HIV.

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• TB prevalence and death rates have probably been
  falling globally for several years.
• In 2005, the TB incidence rate was stable or in
  decline in all six WHO regions, and had reached a
  peak worldwide. However,
• The total number of new TB cases was still rising
  slowly, because the case-load continued to grow
  in the African, Eastern Mediterranean and
  South-East Asia regions.

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• 3. More than 90 million TB patients were reported
  to WHO between 1980 and 2005.
• 26.5 million patients were notified by DOTS
  programmes between 1995 and 2005.
• 10.8 million new smear-positive cases were
  registered for treatment by DOTS programmes
  between 1994 and 2004.

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• A total of 199 countries/areas reported 5 million
  episodes of TB in 2005 (new patients and
  relapses).
• 2.3 million new pulmonary smear-positive patients
  were reported by DOTS programmes in 2005.
• and 2.1 million were registered for treatment in
  2004.

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Detection Rate
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• Almost 60 per cent of TB cases worldwide are now
  detected, and out of those, the vast majority are
  cured. Over the past decade, 26 million patients
  have been placed on effective TB treatment thanks
  to the efforts of governments and a wide range of
  partners. But the disease still kills 4400 people
  every day."

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• Globally, an estimated 9.4 million incident (new)
  cases of TB in 2008.
• Cases occurred in
• WHO South-East Asia Region (55),
• WHO African Region (30),
• WHO Eastern Mediterranean Region (7), WHO
  European Region (5)
• WHO Region of the Americas (3).

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• The five countries with the largest numbers of
  cases in 2008 were
• India (1.62.4 million),
• China (1.01.6 million),
• South Africa (0.380.57 million),
• Nigeria (0.370.55 million)
• Indonesia (0.340.52 million).
• Of the 9.4 million new TB cases in 2008,
• An estimated 1.4 million (15) were HIV
  positive 78 of these HIV-positive cases were in
  the WHO African Region and 13 were in the WHO
  South-East Asia Region.

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• The total number of new cases of TB is increasing
  in absolute terms as a result of global
  population growth.
• The number of cases per capita is falling. The
  rate of decline is slow, at less than 1 per
  year.
• Globally, the rate peaked at 142 cases per 100
  000 population in 2004. In 2008, there were an
  estimated 140 new cases per 100 000 population.
• Incidence rates are falling in five of the six
  WHO regions. The exception is the WHO European
  Region where rates are approximately stable.

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Factors contributing to rise of TB occurrence
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Factors contributing to rise of TB occurrence

• HIV/AIDS
• 15 of deaths among AIDS patients due to TB.
• Poorly managed TB programs
• Wrong treatment regimen and inconsistent or
  partial treatment lead to multidrug resistant TB
  (MDR-TB).
• Movement of people
• Global trade, traveling and migration

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Agent

• Mycobacterium tuberculosis complex
• M. Tuberculosis
• M. bovis
• M. africanum
• M. microti
• M. canetti

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Tuberculosis Bacillus

• Bacillus is thin, somewhat curved, from 1 to 4
  microns in length, with a complex cellular wall
  (lipid core) responsible for its characteristic
  coloration (acid-alcohol-resistant).
• Susceptible to sunlight, heat and dryness.
• Strictly parasitic and airborne slow
  multiplier.

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Reservoir

• Human
• Cattle

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Modes of transmission
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Modes of transmission

• 1-Air-borne droplet nuclei
• 1-5 µ m in diameter.
• remain airborne for long times.
• Factors determining the probability of infection
• No. of organisms expelled
• Conc. of organisms in air
• Length of exposure
• Immune status of exposed person

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• 2-Ingesion of raw milk diary products.
• 3-Direct invasion through wounds

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Immune System Response

• Bacteria invades lung tissue
• White cells surround the invaders and try to
  destroy them.
• Body builds a wall of cells and fibers around the
  bacteria to confine them, forming a small hard
  lump.

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• Bacteria cannot cause more damage as long as the
  confining walls remain unbroken.
• Most infected individuals never progress to
  active TB.
• Most remain latently-infected for life.
• Infection progresses and develops into active TB
  in less than 10 of the cases.

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Incubation period 4-12 weeks.
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Diagnosis

• No single test is diagnostic in all
  situations, but complementary techniques should
  be used to generate complete rapid information.
• Tuberculin test to identify infection
• Acid fast bacilli smear
• Culture
• MMR X-ray
• Genotype (DNA fingerprinting)

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Tuberculin test

• 0.1ml intradermal.
• 48-72 hours
• false negative
• poor nutrition
• poor general health
• overwhelming acute illness
  
• Immunosuppression
• False positive
• BCG vaccination
• Other mycobacteria infection

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Interpretation

• On the basis of sensitivity, specificity and the
  prevalence of TB in different groups three cut
  points have been recommended for defining
  positive tuberculin reaction.
• 5mm. 10 mm. 15 mm.

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Classification of Tuberculosis
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Classification of tuberculosis

• Based on exposure history, infection
  disease.
• Class 0 No history of exposure
• Negative tuberculin test (no
• infection)
• Class 1 History of exposure
• Negative tuberculin

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• Class 2 Positive tuberculin (latent infection)
• Negative X-ray
• Negative bacteriology radiol.
• Class 3 Patients with clinically active TB
• Whose diagnostic procedures
• were completed (positive clinical,
• bacteriological or/and
  radiological
• of current TB).

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• Remain in this stage until treatment is completed
  
• Pulmonary
• Pleural
• Lymphatic
• Bone and/or joint
• Genitourinary
• Miliary
• Meningeal
• Peritonial
• Others

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• Class 4
• -Not clinically active TB
• -Receiving treatment for latent infection
• -Completed previously prescribed
• -course of chemotherapy
• -Abnormal stable radiol. With negative
• bacteriology and positive tuberculin

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• Class 5 Tuberculosis suspect
• -Clinically active disease has not
• been ruled out.
• -Persons not adequately treated
• in the past.
• -Patient should not remain in this
• stage more than 3 months

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Prevention and control
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Prevention and control

• Prevention
• Case finding
• Vaccination
• Chemoprophylasis
• Environmental

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• Control
• Reporting
• Isolation
• Concurrent disinfect ion
• Contact measures
• Treatment

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Elements of the DOTS Strategy

• Political commitment
• Bacteriological diagnostic capacity
• Regular supply ofmedications and supplies
• Directly Observed Treatment Strategy
• Information system

Registries
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• Globally, the rate of treatment success for new
  smear-positive cases in 2007 was 86, exceeding
  for the first time, the global target of 85.
• Eastern Mediterranean (88),
• Western Pacific (92)
• South-East Asia (88)
• African Region and the WHO Region of the Americas
  (79 79)
• WHO European (67)

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• Among the 22 high-burden countries, the 85
  target of treatment success was met or exceeded
  in 13 countries, including, for the first time,
  in Afghanistan.
• The rate of treatment success was also 85 in
  Kenya and 88 in the United Republic of Tanzania,
  showing that countries with high HIV prevalence
  among TB cases are nontheless able to achieve the
  targert.