Global Burden of Disease: An Introduction Kirk R. Smith Professor of Global Environmental Health

Global Burden of Disease: An Introduction Kirk R. Smith Professor of Global Environmental Health

What is health?

• “Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.”

• First of nine principles on first page of World Health Organization Constitution adopted in NYC in July 1946 by 61 nations
• “spiritual well-being” added in 1999 by World Health Assembly, which at that time had 191 member states
• http://www.ldb.org/iphw/whoconst.htm

How would this be operationalized for the following common queries?

• What is the total impact of disease and injury in the population? -- the overall target for public health interventions?

• Which diseases are most important for which groups?
• Are things getting better or worse?

• How do we compare the impacts of different risk factors and potential interventions that affect different populations?

• For example, what is the burden of disease from environmental factors?
• How does the impact of tobacco smoking compare to that from air pollution?

Environmental Health Effects

• Example of results from outdoor air pollution studies

• Asthma attacks
• Missing workdays
• Missing school days
• Days with cough
• Emergency room visits
• Hospital admissions
• Physician visits
• Medication use
• Daily death rate
• Lung function
• Self-reported health status
• Etc.

• How can these be compared across time, cities, countries, age groups, sectors (e.g., transport versus power plants), etc.?

• Let alone compared with the health impacts from completely different risk factors, such as water pollution, lead exposure, high cholesterol, unsafe sex, etc.?

Ultimate Measure of Ill-health?

• Death is most common

• Easy to determine
• Commonly tabulated

• Severe problems as a measure

• Everyone dies
• Health never achieved
• Age is clearly important

• Deaths + Illness = ?

Combined Measure

• What else to use?

• Money? Are you kidding?
• Is used in legal and other realms, but not appropriate for public health

• Most fundamental deprivation is loss of time:

• Same potential life length shared by all humans
• The degree to which a person does not achieve this life length is a measure of ill-health
• Can be used for disabilities, as well, but need to weight relative severity of disabilities as well as tabulate their duration

Health Adjusted Life Years HALY

• Basically the number of fully healthy life years lost to a particular disease or risk factor.

• Considers the age at which the disease or death occurs and the duration and severity of any disability created.

Global Burden of Disease Database

• Developed at Harvard University originally for the World Bank

• Extended greatly in the mid-1990s and now adopted by the World Health Organization

• Updated database published on web each year and summarized in World Health Report

• Dozens of countries now have NBDs

• Even states (provinces) and cities have them, including SF and LA

Need for a C4 Database in Health (Which we have had in many other fields for long periods)

• Combined mortality and morbidity

• Complete

• Much of the world unrepresented in past databases
• Many important disabilities unaccounted

• Consistent definitions of disease states

• Coherent

• Deaths by disease need to add to total
• By age and sex
• Match with demographic stats
• No natural discipline, i.e. no import stats from the afterlife tabulating how many died of what

Disability Adjusted Life Year The DALY, a kind of HALY

• Principle #1: The only differences in the rating of a death or disability should be due to age and sex, not to income, culture, location, social class.

• Principle #2: Everyone in the world has right to best life expectancy in world

• DALY = YLL + YLD

• Years of Lost Life (due to mortality)
• Years Lost to Disability (due to injury & illness)

Years of Lost Life: Examples

What is Meant by “Disability?”

• Impairment: Symptoms at organ level, e.g., broken leg

• Disability: Objective alteration of behavior or performance at the individual level, e.g., cannot walk

• “Handicap”: Changed interaction with others at the social/environmental level, e.g., cannot work

• http://www.disabilityhelper.com/Disability-Impairment-Handicap.htm

Schema for Assessing Non-fatal Health Outcomes

• Disease Impairment

• Polio Paralyzed legs

• Brain Mild mental

• injury retardation

Whom do you ask to determine disability weights?

• Patient

• Family

• Caregiver

• Health professional

• Public health experts

• Public at large

• Insurance companies and lawyers (court cases)

Classes of Disability Weights, with examples

• 1: 0-0.02 Vitiligo on face

• 2: 0.02-0.12 Diarrhea, sore throat

• 3: 0.12-0.24 Radius fracture in stiff cast

• 4: 0.24-0.36 Below the knee amputation

• 5: 0.36-0.5 Down syndrome, COPD

• 6: 0.5-0.7 Unipolar depression, tetanus

• 7: 0.7-1.00 Psychosis, quadriplegia

Top Ten Causes of Disability in 15-44 year olds (2000)

Sample DALY Calculations Diseases A and B

• A. 100,000 children are stricken for 1 week with a disability weighting of 0.3; 2% die at 1 year old.

• B. 100,000 adults are stricken for 2 years with a disability weighting of 0.6; 20% die at 80 years old.

• A: YLL (= 2000 x 80) + YLD (=100k x (7/365) x 0.3) = 160,000 + 575 = 160,600

• B: YLL (= 20,000 x 8) + YLD (=100k x 2 x 0.6) = 160,000 + 120,000 = 280,000

Occam's Razor

• “One should not increase, beyond what is necessary, the number of entities required to explain anything”

• Occam's razor is a logical principle attributed to the 14th Century philosopher William of Occam (or Ockham). The principle states that one should not make more assumptions than the minimum needed. This principle is often called the

• Principle of Parsimony

The DALY Passes Occam’s razor criterion, because it reveals something different from deaths

Examples of Using a C4 database: World DALYS Lost (2000)

Impact of Development on Women and Children

Child Cluster Diseases: the World’s Largest Scandal

• 1.4 million children

• Rates in LDCs are thousands of times those in MDCs (Africa = 4700x that of W. Europe)

• Vaccine coverage in Africa went from 60% in 1990 to 46% in 1999

• Has stayed at 70% in South Asia for many years

Relative Risks between Poor Africa and USA

• Chance of woman dying in childbirth: 400 times greater

• Child dying of diarrhea: 400 times

• Of pneumonia: 500 times

• Of measles: 4000 times

• Similar in South Asia (India, Bangladesh, etc)

Disease Categories

• I - Traditional, Communicable

• Infectious, maternal, perinatal, nutritional

• II - Modern, Non-communicable

• Cancer, heart, neuro-psychiatric, chronic lung, diabetes, congenital

• III - Injuries, Non-Transitional

• Unintentional
• Motor vehicle, poisoning, falls, fire, drowning
• Intentional
• Suicide, violence, war

Classic Epi Transition

• I. Infectious diseases decline during development

• II. Chronic disease rise during development

• III. Injuries show no pattern during development and are thus “non-transitional”

Empirical Test of the Epi Tranistion

• Does it hold up to examination using the first C4 database?

• Classic epidemiologic transition only deals with mortality, thus here termed the “Mortality Transition”

• “Epidemiologic Transition” here applied to same evaluation using DALYs

Epi Transition: Updated

• In terms of actual age-adjusted impact on populations, all classes of disease decline during development

• I. Declines dramatically at every level
• II. Declines slowly, but with little decline seen across middle income regions
• III. Declines in a similar way to II and thus is not “non-transitional”

• Better to be rich for all major types of ill-health, although there are exceptions for individual diseases

Comparison of GBD Estimates for 2005 with GBD for 1990

• Population: 5.3/6.4 billion (+21%)

• Deaths: 50/64 million (+28%)

• DALYs: +7%

• DALYS/capita: -11%

• I = 44/38.5%;

• II = 41/48.9%;

• III = 15/12.5%

Changes in Important Diseases: 1990-2005 What is happening with each?

• Diarrhea: 7.3/3.9% (-42% in absolute terms)

• ARI: 8.5/5.9% (-25%)

• Malaria: 2.3/2.3% (-6%)

• Lung Cancer: 0.65/0.8% (+32%)

• TB: 2.8/2.1% (-18%)

• HIV: 0.8/5.6% (7.4 times as much)

• Depression: 4.7/5.8 (+29%)

Can we reach public health?

• Is there a absolute value of health (lost DALYs) beyond which society does not have an obligation to exceed?

• Is there a cost per unit improvement in health ($ per DALY) above which society does not benefit from further expenditure?

Entry into GBD databases

• Best single modern book covering the GBD and CRA ideas, methods, and results, but without full detail and sophistication/complexity:  Global Burden of Disease and Risk Factors, (Lopez, Mathers, Ezzati, Jamison, Murray) Oxford University and World Bank Presses, 2006.  475 pp.  Fully downloadable at http://www.dcp2.org/pubs/GBD which also has links to data used in the book.

• Best single page to find GBD data divided by world regions defined in several ways (WHO regions, World Bank regions, income groups etc.) for 2004. http://www.who.int/healthinfo/global_burden_disease/2004_report_update/en/index.html

• For projections to 2030 and links to dozens of other publications, see http://www.who.int/healthinfo/global_burden_disease/en/index.html

• The full set of background materials and pubs of the previous (2004) Comparative Risk Assessment (CRA) covering 26 major risk factors, environmental and other: http://www.who.int/healthinfo/global_burden_disease/cra/en/index.html

• Full databases for the previous CRA study: http://www.who.int/healthinfo/global_burden_disease/risk_factors/en/index.html

• Description of the GBD/CRA 2005 Revisions now underway: http://www.who.int/healthinfo/global_burden_disease/GBD_2005_study/en/index.html