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Measuring the burden of tuberculosis

Estimates of the incidence of tuberculosis (TB) and TB-related mortality are key indicators in the evaluation of B-control activities. But how are these estimates derived? The presentation highlights the key methods, and focuses on the uncertainties around the estimates.

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Measuring the burden of tuberculosis

  1. 1. The burden of tuberculosis : Measuring uncertainty F R AN K VAN L E T H A S S O C I A T E P R O F E S S O R O F G L O B A L H E A L T H A M S T E R D A M U N I V E R S I T Y M E D I C A L C E N T E R S , U N I V E R S I T Y O F A M S T E R D A M A M S T E R D A M I N S T I T U T E F O R G L O B A L H E A L T H A N D D E V E L O P M E N T C H A I R T B n e t
  2. 2. www.aighd.org More TB than ever?
  3. 3. www.aighd.org More TB than ever?
  4. 4. www.aighd.org WHO strategy and targets
  5. 5. www.aighd.org Burden of tuberculosis Key information to evaluate TB control strategies Measurement methods develop and change over time ◦ Old estimates are updated regularly Previous WHO reports no longer digitally available
  6. 6. MEASURING TB INCIDENCE
  7. 7. www.aighd.org Definition and measurement The number of new cases per time period
  8. 8. www.aighd.org TB incidence Direct Surveys Notification Definition and measurement The number of new cases per time period
  9. 9. www.aighd.org Measuring TB incidence: direct Assess TB
  10. 10. www.aighd.org Measuring TB incidence: direct Assess TB
  11. 11. www.aighd.org Measuring TB incidence: indirect Assess TB migration death Assess TB
  12. 12. www.aighd.org Measuring TB incidence: indirect Assess TB migration death Assess TB
  13. 13. www.aighd.org Measuring TB incidence: indirect Assess TB Assess duration of disease Incidence = Prevalence / duration
  14. 14. www.aighd.org TB prevalence surveys
  15. 15. www.aighd.org Surveys with low or medium TB prevalence 87,000 participants Ukraine 17,400 cultures 97 patients
  16. 16. www.aighd.org Surveys with low or medium TB prevalence 134,000 participants Russia 26,800 cultures 83 patients
  17. 17. www.aighd.org Surveys with low or medium TB prevalence 84,000 participants Moldova 16,800 cultures 99 patients
  18. 18. www.aighd.org Surveys with low or medium TB prevalence 83,000 participants Romania 16,600 cultures 100 patients
  19. 19. www.aighd.org Surveys with low or medium TB prevalence 845,000 participants Denmark 169,000 cultures 67 patients
  20. 20. www.aighd.org Measuring TB incidence: Notification
  21. 21. www.aighd.org Measuring TB incidence: Notification Incidence = notification Incidence = notification * correction factor Incidence = notification * opinion
  22. 22. www.aighd.org Expert opinion: The onion model All cases Access Presenting Diagnosed Reordered
  23. 23. www.aighd.org Consensus on notification
  24. 24. www.aighd.org Reaching consensus Subjective Open discussion not always possible Error prone due to “blind spots” Example of Tanzania ◦ WHO: 48% of cases notified ◦ Programme: 85% cases notified ◦ Applied on next year data: case detection > 100%
  25. 25. www.aighd.org Capture-Recapture analysis 25 Peterson, 1894
  26. 26. www.aighd.org Capture Recapture analysis Source 1 Source 2 Total Present Absent Present X11 X10 n2 Absent X01 X00 Total n1 N N ^ = (n1 +1)(n2 +1) (Xii +1)
  27. 27. www.aighd.org Example The Netherlands van Hest, 2007 Not notified 13%
  28. 28. www.aighd.org Capture-recapture analysis Requires multiple independent sources Matching patients from different sources is often problematic ◦ Data protection laws Can be repeated once system has been set up
  29. 29. www.aighd.org Methods used by World Health Organization (WHO) WHO, 2018
  30. 30. MEASURING TB MORTALITY
  31. 31. www.aighd.org WHO strategy and targets
  32. 32. www.aighd.org Measuring mortality Count causes of death 17th Century, John Graunt
  33. 33. www.aighd.org Measuring mortality
  34. 34. www.aighd.org Measuring mortality Potential sources ◦ Vital registration ◦ Verbal autopsies ◦ Mortality surveys ◦ Estimates: incidence * case fatality rate Problems ◦ Absence of vital registration systems ◦ Classification / attribution ◦ Coverage / generalizability
  35. 35. www.aighd.org Measuring TB mortality WHO, 2018
  36. 36. www.aighd.org TB mortality: Different estimates TB mortality estimates ◦ WHO ◦ IHME (Global Burden of Disease project)
  37. 37. www.aighd.org Garcia-Basteiro, 2017
  38. 38. www.aighd.org Difference TB mortality estimates
  39. 39. CONCLUSIONS
  40. 40. www.aighd.org Conclusions Estimating TB burden requires multiple methods Estimates are done with uncertainty More precise estimates require improved surveillance and vital registration systems Full insight in TB burden requires adequate ◦ Identification patients with presumptive TB ◦ Proper diagnostic procedures ◦ Complete reporting and notification to national bodies ◦ Timely reporting to international organizations (WHO)
  41. 41. Thank you for the attention slides posted on frankvanleth.com

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Estimates of the incidence of tuberculosis (TB) and TB-related mortality are key indicators in the evaluation of B-control activities. But how are these estimates derived? The presentation highlights the key methods, and focuses on the uncertainties around the estimates.

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