What is epidemiology?. GIS and health geography Major applications for GIS Epidemiology What is...
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What is epidemiology?. GIS and health geography Major applications for GIS Epidemiology What is health (and how location matters) What is a disease (and
GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 3
A GIS can be a useful tool for health researchers and planners
because, as expressed by Scholten and Lepper (1991): Health and
ill-health are affected by a variety of life- style and
environmental factors, including where people live. Characteristics
of these locations (including socio- demographic and environmental
exposure) offer a valuable source for epidemiological research
studies on health and the environment. Health and ill-health always
have a spatial dimension, therefore. More than a century ago,
epidemiologists and other medical scientists began to explore the
potential of maps for understanding the spatial dynamics of
disease.
Slide 4
1.Spatial epidemiology 2.Environmental hazards 3.Modeling
Health Services 4.Identifying health inequalities
Slide 5
Spatial epidemiology is concerned with describing and
understanding spatial variation in disease risk. Individual
Individual level data small areas Counts for small areas Recent
developments owe much to: Geo-referenced health and population data
Computing advances Development of GIS Statistical methodology
Slide 6
Population is unevenly distributed geographically. People move
around (day-to-day movements; longer term movements including
migration). People possess relevant individual characteristics
(age, sex, genetic make-up, lifestyle, etc). small areas People
live in communities (small areas).
Slide 7
Provides a qualitative answer about the existence of an
association (e.g. between environmental variable and health
outcome). May provide evidence that can be followed up in other
ways.
Slide 8
These studies typically involve examining geographical
variations in exposure to environmental variables (air, water,
soil, etc.) and their association with health outcomes while
controlling for other relevant factors using regression.
Slide 9
Slide 10
Frequency and quality of population data (e.g. Census every
5/10 years). Spatial compatibility of different data sets.
Availability of data on population movements. Measuring population
exposure to the environmental variable. Environmental impacts are
often likely to be quite small (relative to, for example, lifestyle
effects) and there may be serious confounding effects. Cannot
estimate strength of an association. Ecological (or aggregation)
bias.
Slide 11
Allow for heterogeneity of exposure. Use well defined
population groups. Use survey data to help obtain good exposure
data. Allow for latency times. Allow for population movement
effects. (Richardson 1992)
Slide 12
Dr. John Snows Map of Cholera Deaths in the SOHO District of
London, 1854
Slide 13
1.Spatial epidemiology 2.Environmental hazards 3.Modeling
Health Services 4.Identifying health inequalities
Slide 14
Hazard Surveillance Hazardous agent present in the environment
Route of exposure exists Exposure Surveillance Host exposed to
agent Agent reaches target tissue Agent produces adverse effect
Outcome Surveillance Effect clinically apparent
Slide 15
GIS: Identify causal and mitigating factors
Slide 16
1.Spatial epidemiology 2.Environmental hazards 3.Modeling
Health Services 4.Identifying health inequalities
Slide 17
A generic index of accessibility/ remoteness for all populated
places in non-metropolitan Australia. A model which allows
accessibility to any type of service to be calculated from all
populated places in Australia.
Slide 18
Slide 19
Where do infants and children die in WA? 1980-2002 Jane
Freemantle, PhD. November 2004
Slide 20
Identifying health inequalities: Well-known relationship 25%
50% of observed gradient due to risk factors like smoking,
hypertension and diabetes in lower socio-economic groups (Marmot et
al.,1997) Access to healthcare (Bosma et al., 2005) Imbalance
between workplace demands and economic reward (Lynch et al.,1997)
Poor education, lower levels of health literacy, low birth weight
(Marmot, 2000) Relationship may vary with gender, with the
association thought to be stronger in males (Thurston, 2005)
Slide 21
Number of daily hospital discharges (Y) with Ischemic Heart
Disease (IHD) where admission had been via emergency room for 591
postcodes in NSW Every day from July 1, 1996 to June 30, 2001 Males
and females 5-year age increments Denominator (N) obtained from
census Social disadvantage measured at postal area level using the
census-derived SEIFA (Socio-Economic Indexes for Areas) index
Slide 22
High values indicate social advantage
Slide 23
Slide 24
GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 25
The study of the distribution and determinants of health and
disease-related states in populations, and the application of this
study to control health problems. the product of [epidemiology] is
research and information and not public health action and
implementation (Atwood et al. 1997) epidemiologys full value is
achieved only when its contributions are placed in the context of
public health action, resulting in a healthier populace. (Koplan et
al. 1999)
Slide 26
(H. Shodell, Science 82, September, p. 50) are like bookies of
disease, stalking the globe to determine point-spreads on which
groups of people are most likely to get which diseases. Part
detective and part statistician, part anthropologist and part
physician, epidemiologists hope to track down the agents of illness
by deducing which of the differences between peoples lie at the
root of their distinctive disease patterns.
Slide 27
DESCRIPTIVE Health and disease in the community What? Who?
When? Where? What are the health problems of the community? What
are the attributes of these illnesses? How many people are
affected? What are the attributes of affected persons? Over what
period of time? Where do the affected people live, work or spend
leisure time? ANALYTIC Etiology, prognosis and program evaluation
Why? How? What are the causal agents? What factors affect outcome?
By what mechanism do they operate?
Slide 28
Dorland's Illustrated Medical Dictionary (28th ed.): Health "a
state of optimal physical, mental, and social well-being, and not
merely the absence of disease and infirmity. Disease "any deviation
from or interruption of the normal structure or function of any
part, organ, or system (or combination thereof) of the body that is
manifested by a characteristic set of symptoms and signs...".
Slide 29
Health, as defined in the World Health Organization's
Constitution, is "a state of complete physical, mental and social
well-being and not merely the absence of disease or infirmity."
Health is seen as more than just the absence of disease, and
depends upon a complex suite of factors, with location taking the
lead. A location is more than just a position within a spatial
frame (e.g., on the surface of the Earth or within the human body).
Different locations on Earth are usually associated with different
profiles: physical, biological, environmental, economic, social,
cultural and possibly even spiritual profiles, that do affect and
are affected by health, disease and healthcare.
Slide 30
An example of how location matters and carries with it other
factors into play: The body weight of infants at birth is one
readily available piece of data, and the relationship between low
birth-weight and maternal and child health is a continuing line of
research. In New York City, Sara McLafferty and Barbara Tempalski
have studied the spatial distribution of low birth-weight infants
and identified areas in which the number of low birth-weight
infants increased sharply during the 1980s. Their results indicated
that the rise in low birth-weight was closely linked to women's
declining economic status, inadequate insurance coverage and
prenatal care, as well as the spread of crack/cocaine.
Slide 31
Slide 32
Slide 33
GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 34
Manifestional criteria: labeling symptoms Manifestational
criteria refer to symptoms, signs, and other manifestations of the
condition. Defining a disease in terms of manifestational criteria
relies on the proposition that diseases have a characteristic set
of manifestations. This defines disease in terms of labeling
symptoms. Causal criteria: underlying pathological etiology Causal
criteria refer to the etiology of the condition, which must have
been identified in order to be employed. This defines disease in
terms of underlying pathological etiology.
Slide 35
How do you identify a disease? The Acquired Immunodeficiency
Syndrome (AIDS) was initially defined by the CDC in terms of
manifestational criteria as a basis for instituting surveillance.
The operational definition grouped diverse manifestations Kaposi's
sarcoma outside its usual subpopulation, PCP and other
opportunistic infections in people with no known basis for
immunodeficiency. This was based on similar epidemiologic
observations (similar population affected, similar geographical
distribution) and a shared type immunity deficit (elevated ratio of
T-suppressor to T-helper lymphocytes).
Slide 36
Human immunodeficiency virus (HIV, previously called human
lymphotrophic virus type III) was discovered and demonstrated to be
the causal agent for AIDS. AIDS could then be defined by causal
criteria.
Slide 37
A single causal agent may have multiple clinical effects.
Multiple etiologic pathways may lead to apparently identical
manifestations, so that a manifestationally- defined disease entity
may include subgroups with differing etiologies. Multi-causation
necessitates a degree of arbitrariness in assigning a causative
versus a contributing factor to a disease. Not all persons with the
causal agent develop the disease.
Slide 38
Underlying Genetic Susceptibility Onset of disease Diagnosis of
disease Environmental & Behavioral Factors (Spatial dependence)
Physiologic Abnormalities Clinical disease Cause-specific mortality
X Sub-clinical disease
Slide 39
GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence versus prevalence Identifying the population Working with
small area data
Slide 40
To study disease, we need measures of its occurrence. Some
measures of disease occurrence Counts Prevalence Incidence
Mortality
Slide 41
DESCRIPTIVEHealth and disease in the community What? Who? When?
Where? What are the health problems of the community? What are the
attributes of these illnesses? How many people are affected? What
are the attributes of affected persons? Over what period of time?
Where do the affected people live, work or spend leisure time? Each
of the measures can be calculated for different combinations of
What? Who? When? and Where? Each of the Ws needs to be defined
carefully to get comparable measures across a province or state, a
nation, the world.
Slide 42
The prevalence of a disease is the proportion of individuals in
a population with the disease (cases) at a specific point in time:
Prevalence is a proportion range of 0 to 1 Removes the effect of
total population size makes estimates from different populations or
over time more comparable.
Slide 43
Often expressed as a percent (%) Prevalence * 100 Also often
expressed as the prevalence per 1,000 or 10,000 or 100,000.
Prevalence * 1,000 = prevalence per 1,000.