Disease Classification, morbidity, mortality.

1. Summer Course:Introduction to Epidemiology August 25, 1100-1230 Disease Classification, morbidity, mortality. Dr. N. Birkett, Department of Epidemiology & Community Medicine, University of Ottawa

2. Session Overview • Review basis of disease classification systems • Overview main measures of mortality and morbidity. • Sources of information about mortality/morbidity in Canada.

3. Traditional Epidemiology Questions • Who gets disease ‘X’? • Why did someone get disease ‘X’? • What is going to happen to someone who has disease ‘X’? • What can we do to prevent someone getting disease ‘X’? • What can we do to help someone with disease ‘X’? • Why are more (or fewer) people getting disease ‘X’ now than before? • Why do people living in ‘Y’ get more (or less) of disease ‘X’ than people living in ‘Z’?

4. Classification (1) • To answer questions like these, we need to be able to group or classify people with similar conditions. • This can be a hard task • Focus on similarities • Place ‘similar things’ in the same group • Focus on differences • Place ‘different things’ in different groups • Classifications vary in the extent of heterogeneity vs. homogeneity • E.g. Psychiatry vs. cancer

5. Classification (2) • John Graunt (1662) • Grouped deaths into common causes. • E.g. old age, consumption, smallpox, plague, diseases of teeth, worms • James Farr (1860’s) • Developed an early disease classification system. • Became the foundation for our current system.

6. Classification (3) • What features could be used as basis for classification? • Site of disease • Hot vs. cold • Yin/yang • Imbalance of humours • Behaviour vs. psychological constructs vs. biological neural factors • And so on. • These create different ‘diseases’. • They are not different ways to classify things into the ‘real’ disease groupings.

7. Classification (4) • Main disease classification is the International Classification of Diseases and Related Health Problems (ICD). • Developed from Farr’s work • First ICD version created around 1900. • Up-dated about every 10 years. • Current version: ICD-10 • ICD-9 is still widely used in epidemiology

8. Classification (5) • ICD-10 • 21 major Chapters. • Each chapter is divided into paragraphs and sub-sections. • Largely based on traditional diagnostic groupings but includes ‘external’ and other causes. • C34.4 – Lung cancer, lower lobe • I60.4 – Subarachnoid hemorrhage, basilar artery • V95.4 – Spacecraft accident injuring occupant

9. Classification – ICD10 (6) I. Infections and Parasitic Diseases (A-B) II. Neoplasms (C-D) III. Diseases of blood &blood-forming organs (D) IV. Endocrine, nutritional and metabolic Diseases(E) V. Mental & Behavioural Disorders (F) VI. Diseases of the Nervous System (G) VII. Diseases of the eye and adnexa (H) VIII. Diseases of the Ear and Mastoid (H) IX. Diseases of the Circulatory System (I) X. Diseases of the Respiratory System (J) XI. Diseases of the Digestive System (K)

10. Classification – ICD10 (7) XII. Diseases of the skin (L) XIII. Diseases of the musculoskeletal system (M) XIV. Diseases of the Genitourinary system (N) XV. Pregnancy, childbirth, etc. (O) XVI. The Perinatal period (P) XVII. Congenital conditions, etc. (Q) XVIII. Symptoms, signs, NOS (R) XIX. Injury, poisoning (S-T) XX.External causes (V-Y) XXI. Factors influencing health status and contact with health services (Z)

11. Classification (8) • Many other classification systems exist • Cancer • ICDO • Snomed • DSM-IV • New version (V) is creating great controversy • “includes new disorders and milder versions of old ones that will lead to pathologizing normal behaviour.” • Will increase use of psychoactive drugs • Impairments and disabilities • Conditions in Primary Care

12. Vital Statistics • Information on main life events • Births • Deaths • Marriages • Usually collected at the local (municipal) level). • Reports sent to provincial government • Federal government (Statistics Canada) collates information into reports.

18. Mortality & morbidity measures (1) • Prevalence • More correctly: point prevalence • Similar to results from a political poll. • The probability that a person has a disease or condition TODAY. There is no time dimension. • ‘The prevalence of hepatitis C in intravenous drug users in Ottawa is 60%.’. • This means that 60% of intravenous drug users in Ottawa have Hepatitis C.

19. Mortality & morbidity measures (2) • Incidence (general) • Measures the development of NEW cases of a disease or condition. • Requires a time dimension. • If not given, ‘one year’ is often the implicit time period. • Two types of incidence are recognized • Cumulative incidence or incidence proportion • Incidence rate or incidence density • Sorting out the two types of incidence is tricky and somewhat advanced. • I’ll give you a simplified approach.

20. Mortality & morbidity measures (3) • Cumulative incidence or Incidence proportion • Measures the probability of developing a NEW case of a disease or condition in a set period of time. • ‘The cumulative incidence of esophageal cancer in adults is 4/100,000 in one year.’ • The probability that an adult will develop esophageal cancer in the next year is 4/100,000

21. Incidence rate (the hard one) Measures the rate at which people develop a NEW case of a disease or condition. Person-time = (# people) X (time spent at risk) Able to allow for ‘loss to follow-up’. This is not a probability. Can take on any value from 0 to +∞. Has units: time-1 or cases/person-year. ‘The Incidence Rate of influenza is 4 cases per 100 person-years’. Mortality & morbidity measures (4)

22. Mortality & morbidity measures (5) • Commonly used ‘rates’ • The word ‘Rate’ is used very loosely in epidemiology. • You need to know from context what is meant (e.g. prevalence rate isn’t a real ‘rate’). • When used correctly, three broad labels can be applied to ‘rates’. • Crude • Specific • Adjusted or standardized

23. Crude mortality rate (crude death rate) Mid-year population is usually used for denominator The simplest rate in epidemiology. Mortality & morbidity measures (6)

24. Cause-specific mortality rate: Can also be specific to ‘sex’, ‘geography’, ‘age’, etc. Mortality & morbidity measures (7)

25. Mortality & morbidity measures (8) • Age-standardized mortality rate • A fictitious rate designed for comparing groups which differ in their age distribution • The crude mortality is higher in Canada than in Sierra Leone. • Is the risk of dying really higher in Canada • OR is this due to the fact that the population in Sierra Leone is younger? • Will be discussed more on Friday. For now, just learn the name and purpose. • Can be adjusted for factors other than age.

26. Crude Birth Rate General Fertility Rate Some important rates (1)

27. Some important rates (2) Total Fertility Rate • Average number of children who would be born alive to a woman during her lifetime IF she were to pass through all her child bearing years conforming to the age-specific fertility rates in the current year. • Complex! Essentially, it estimates the number of children born to a woman which would be expected if the current fertility patterns applied through-out her life

28. Some important rates (3) Completed Fertility • Average number of life births per woman who has reached the end of her child bearing period. • Similar to Total Fertility Rate but is based on the actual fertility rates through-out a woman’s life-time rather than on assuming the rates are the same today. • Now, let’s consider this graph:

30. Some important rates (4) • Traditionally, epidemiology has lots of rates related to pregnancy and child development • Due to importance of childbirth and the very bad outcomes in previous centuries • We’ll look at • Infant Mortality Rate • Maternal Mortality Rate • Various still birth and related rates.

31. Infant Mortality Rate Excellent indicator of public health services. High rates indicate unmet health/environmental conditions Nutrition; sanitation; education Widely used for international comparisons Canada (2001): 4.9/1,000 Sierra Leone: >100/1,000 Some important rates (5)

32. Maternal Mortality Rate Can be strongly influenced by illegal abortions. Increases with maternal age In Canada, any maternal death is most likely due to medical negligence Canada: 0.3/100,000 Sierra Leone: 450/100,000 Some important rates (6)

34. Some important rates (7) Live birth • Complete expulsion from the mother of a product of conception which breathes or otherwise show any sign of life after expulsion. One breath is enough. But, the umbilical cord must have been cut. Fetal Death • A death of the product of conception prior to the complete expulsion. There must be no sign of life post-expulsion. These definitions are controversial and not consistently used (e.g. early miscarriages; therapeutic abortions).

35. Some important rates (8) Stillbirth • There are at least three definitions used: • A fetal death occurring after a gestation of at least 20 weeks. • A fetal death occurring after a gestation of at least 28 weeks (the WHO definition when I last checked) • A fetal death occurring after a gestation of at least 20 weeks or with a fetus weighing more than 500 grams • Variation partly due to improvements in neonatal care/survival.

38. Some important rates (9) Life expectancy • Not really a rate but it fits in here. • The number of years which a person can expect to live • Usually reported by the media as “life expectancy at birth” (about 79 for men and 82 for women) • Can be used at any age. • Life expectancy at age 50 is the number of additional years the person can expect to live given they have survived to age 50.

39. Some important rates (10) Life expectancy (cont) • Computation is complex and uses life tables. We won’t get into this process in this course • Life Expectancy is strongly affected by deaths in early childhood • This is the main reason why life expectancy was so low pre-1900 and is still low in developing countries • After reaching adulthood, there is less discrepancy between countries

40. UK data

41. Some important rates (11) Life expectancy (cont) • Why the increase over the 1900’s? • Marked reduction in early childhood mortality • Nutrition • Sanitation • Immunization • Decrease in infectious disease mortality • Nutrition • Sanitation • Housing • Immunization • antibiotics

42. Sources of data: mortality (1) Vital Statistics • Births, deaths, marriages, etc. • Mostly reported by physicians. • Coded centrally by staff trained to apply ICD, etc. coding. • Accuracy of information depends on initial effort by person completing the form • Multiple causes of death coding. • Timeliness of reports is getting better • 2009 data is available on-line through Statistics Canada.

43. Sources of data: mortality (2) Canadian Mortality Data-base • Information from all Canadian death certificates from 1950 to present. • Death certificates (and birth certificates) used to be publicly available but are not now. • CMDB can be searched electronically (for a fee) to link subjects to mortality records • ‘GIRLS’ • Completeness is very good • mainly misses out-of-country deaths.

44. Sources of data: morbidity (1) Much harder to get information and much less complete (e.g. many diseases/conditions have no routinely available information) • Good information on • Many infectious diseases • Cancer • Abuse and violence • Some information, but lower quality, on: • Congenital abnormalities • Vision problems • Diabetes • Surprisingly poor information on CHD incident cases.

45. Sources of data: Morbidity (2) Potential sources of information • Disease registries • Surveillance • Reportable diseases • Administrative data • CIHI • ICES • Saskatchewan Drug Programme • ADRs • General population surveys • Special targeted surveys

46. Sources of data: morbidity (3) Registries • Attempt to provide a complete listing of all people with a pre-defined condition or illness • Most are voluntary, leading to incomplete capture and potential bias • Most extensive and successful with cancer. • Cancer registration is mandated by law

47. Sources of data: morbidity (4) Registries: Subject Identification • Passive vs. active vs. other. • Passive • Subjects identified using existing records with no active reporting by MD, patient, etc. • Active • MD required to report any one with the diagnosis • Other • Volunteers • Members of patient support groups • CNIB • Canadian Diabetes Association

48. Sources of data: morbidity (5) Registries: Cancer • Under provincial jurisdiction • Mostly, passive identification • Electronic reporting of new cases. • Since 1969, all provinces send data to Statistics Canada for entry in Canadian Cancer Registry. • Data is usually 3-4 years behind. • Can be used for record linkage • Ethical and privacy issues

49. Sources of data: morbidity (6) Registries: Congenital Diseases • BC has most extensive system (Health Status Registry) • First established in 1952 as voluntary registry of ‘crippled children’ to assist in identifying care needs. • Expanded to include genetic conditions and birth problems like rubella • Now captures cases based on hospital discharge summaries. • Good data since 1984, especially for conditions diagnosed at birth. • Alberta has a less extensive registry (age<1)

50. Sources of data: morbidity (7) Registries: Cardiovascular Disease • No comprehensive CHD registries in Canada • Several groups have local registries of specific conditions • Acute MI patients • Pacemakers • Hard to identify cases • Clinical disease vs. atherosclerosis • Sudden death • Non-hospital treatment • Nova Scotia, Saskatchewan and BC have best information