disease classification, morbidity, mortality. dr. n. birkett, department of epidemiology &...

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DISEASE CLASSIFICATION, MORBIDITY, MORTALITY.

Dr. N. Birkett,

Department of Epidemiology & Community Medicine,

University of Ottawa

SUMMER COURSE:INTRODUCTION TO

EPIDEMIOLOGY

AUGUST 25, 1100-1230

5/6/2014

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Session Overview

Review basis of disease classification systems

Overview main measures of mortality and morbidity.

Sources of information about mortality/morbidity in Canada.

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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’?

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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

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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.

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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.5/6/2014

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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

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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

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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)

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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)

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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

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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.

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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.

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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.

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Mortality & morbidity measures (3)

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Cumulative incidence or Incidence proportion Measures the probability of developing a

NEW case of a disease or condition in a set period of time.

Has no units (it is a probability) ‘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

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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)

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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

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Crude mortality rate (crude death rate)

Mid-year population is usually used for denominator

The simplest rate in epidemiology.

Mortality & morbidity measures (6)

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Cause-specific mortality rate:

Can also be specific to ‘sex’, ‘geography’, ‘age’, etc.

Mortality & morbidity measures (7)

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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.

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Crude Birth Rate

General Fertility Rate

Some important rates (1)

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Some important rates (2)

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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

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Some important rates (3)

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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:

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Some important rates (4)

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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.

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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)

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Some important rates (6)

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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

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Some important rates (7)

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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).

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Some important rates (8)

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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.

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Some important rates (9)

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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.

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Some important rates (10)

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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

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UK data

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Some important rates (11)

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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

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Sources of data: mortality (1)

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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.

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Sources of data: mortality (2)

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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.

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Sources of data: morbidity (1)

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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.

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Sources of data: Morbidity (2)

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Potential sources of information Disease registries Surveillance Reportable diseases Administrative data

CIHI ICES Saskatchewan Drug Programme ADRs

General population surveys Special targeted surveys

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Sources of data: morbidity (3)

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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

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Sources of data: morbidity (4)

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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

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Sources of data: morbidity (5)

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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

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Sources of data: morbidity (6)

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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)

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Sources of data: morbidity (7)

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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

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Sources of data: morbidity (8)

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Registries: Renal failure Canadian Renal Failure Registry

Started in 1981. Voluntary Appears to have been replaced by a broader

based registry collecting cases through hospital discharge summaries:

Canadian Organ Replacement Registry Records information on vital organ transplants

and dialysis patients. Run through CIHI

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Sources of data: morbidity (9)

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Registries: Miscellaneous Vision

CNIB used to run a voluntary registry of people who were legally blind (started in 1918)

Current status unclear. Ottawa Eye Institute is currently doing a review of

vision-related registries Diabetes Mellitus

Montreal-based registry of IIDM started in 1981 Canadian Diabetes Association maintains record of

members but also includes family and non-patients.

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Sources of data: morbidity (10)

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Registries: Miscellaneous Hemophillia

Canadian Hemophillia Society maintains list of people with hemophillia

Trauma, winter sports injuries, childhood injuries, etc. Many are based on hospital discharge information

from CIHI Variable quality but can be useful.

Very limited information on mental health and conditions like arthritis

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Sources of data: morbidity (11)

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Disease surveillance The PHAC runs a large number of surveillance

programmes. Influenza Fluwatch: 2013-14 HIV Injuries West Nile disease

Quality of information can be questioned Incomplete coverage

FluWatch URL: http://www.phac-aspc.gc.ca/fluwatch/index-eng.php

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Sources of data: Morbidity (12)

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Disease surveillance Reportable Diseases

List of specific medical conditions ‘active’ surveillance

MD’s must report (by law) any diagnosis of these conditions Applies mainly to infectious diseases Also applies to

suspected child abuse. Gun shot victims in hospitals (Ontario) Many professional duties

E.g. drug abuse in MD’s.

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Sources of data: morbidity (13)

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Clinical Data: hospital separations Based on discharge diagnoses. Largely managed by the Canadian Institute

for Health Information (CIHI) except for Quebec data.

Provides extensive information on service utilization, costs, procedures, etc.

Limited data on non-hospitalized patients.

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Sources of data: Morbidity (14)

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CIHI (Canadian Institute for Health Information) An independent, not-for-profit organization that

provides essential data and analysis on Canada’s health system and the health of Canadians

Manages multiple data bases Health Human Resources Health Spending Health Services

Multiple sources of information including hospital discharges.

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Sources of data: morbidity (15)

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Clinical Data: OHIP, etc. Contains information included in CIHI but also

information on clinical encounters outside hospital

ICES – Institute for Clinical Evaluative Services Funded by Ontario government Aim is to improve delivery of health care Ontario

residents. Can collaborate with outside groups but strong

security restrictions on access to data.

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Sources of data: Morbidity (16)

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Surveys Can be targeted at specific conditions

(e.g. Canadian Hypertension Survey) or more general (e.g. National Population Health Survey)

Most recent surveys in Canada have based on self-reported data Inaccurate/incomplete diagnoses Focus on risk behaviours and psychosocial

factors

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Sources of data: Morbidity (17)

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Surveys Nutrition Canada Survey (1970-72) Canada Health Survey (1978) Canadian Heart Health Survey (1988-92) Canadian Study on Health and Aging

(1992) NPHS (1994, 1996/6 & 1998/9)

Includes a cohort follow-up component

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Sources of data: Morbidity (18)

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Surveys Canadian Community Health Survey

Started in 2000 Health determinants Health status Health services utilization

2 year cycle 130,000 subjects in year 1 of cycle 35,000 subjects in year 2 of cycle

No physical measures

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Sources of data: Morbidity (19)

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Surveys Canadian Health Measures Survey

N=5,000 Physical measures

Anthropometry Cardio fitness Musculoskeletal fitness Physical Activity Spirometry Oral Health

Blood and urine samples

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Sources of data: morbidity (20)

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Canadian Cohort Studies A number of large-scale cohorts are just getting

started. Cancer CHD The Tomorrow Project Ontario Health Study

Healthy Aging Childhood development

Issues with population representativeness.

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Summary

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ICD-10 is main classification system used Good information on mortality and cancer

incidence Up-to-date numbers can be hard to obtain. Lack of information for several key health

conditions Heart disease incidence Most chronic diseases with non-fatal impact (e.g.

arthritis) Reportable diseases help monitor and control

infectious diseases

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Sources of data: Morbidity (6)

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CIHI Sample databases: Canadian Medication Incident Reporting and Prevention

System Continuing Care Reporting System Discharge Abstract Database Home Care Reporting System Hospital Mental Health Database Hospital Morbidity Database National Ambulatory Care Reporting System Therapeutic Abortions Database National Health Expenditures Database National Prescription Drug Utilization Information System

Largely based on discharge diagnoses and information

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Sources of data: Morbidity (7)

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CIHI Sample registries: Canadian Joint Replacement Registry Canadian Organ Replacement Registry

Linked to kidney registry National Trauma Registry Ontario Trauma Registry