GIS and Health Geography

GIS and Health Geography What is epidemiology?

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 TOC

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. GIS and health Geography

Spatial epidemiology • Environmental hazards • Modeling Health Services • Identifying health inequalities Major applications for GIS

Spatial epidemiology is concerned with describing and understanding spatial variation in disease risk. • Individual level data • Counts for small areas • Recent developments owe much to: • Geo-referenced health and population data • Computing advances • Development of GIS • Statistical methodology Spatial epidemiology

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). • People live in communities (small areas). Framework for analysis

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. Why small area analyses?

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. Geographical correlation studies

Issues: Spatial misalignment

Frequency and quality of population data (e.g. Census every 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. Issues: Uncertainty

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 movementeffects. Issues: Best practices (Richardson 1992)

Dr. John Snow’s Map of Cholera Deaths in the SOHO District of London, 1854 Spatial epidemiology

Environmental hazards

GIS: Identify causal and mitigating factors Environmental hazards

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 ARIA (Accessibility/Remoteness Index of Australia)

AIRA

“Where do infants and children die in WA? 1980-2002” Jane Freemantle, PhD. November2004 Mortality rate of infants (1980-2001)

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) SES and Heart disease

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 The Data

High values indicate social advantage SEIFA distribution in NSW

NSW IHD rates

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) • ‘epidemiology’s 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) What is epidemiology?

… 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. Epidemiologists . . . (H. Shodell, Science ’82, September, p. 50)

What are the health problems of the community? What are the attributes of these illnesses? Etiology, prognosis and program evaluation ANALYTIC Why? How? DESCRIPTIVE Health and disease in the community What? Who? When? Where? 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? By what mechanism do they operate? What are the causal agents? What factors affect outcome? Epidemiologic approaches

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 . . .". What are “disease” and “health”?

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. What is ‘health’

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. Location and health

Location and health

Manifestional criteria: 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: 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. What is ‘disease’

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). Manifestational Criteria

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. Causal Criteria

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. Challenges with Disease Classifications

Onset of disease Diagnosis of disease Cause-specific mortality Physiologic Abnormalities Clinical disease Sub-clinical disease Underlying Genetic Susceptibility X Environmental & Behavioral Factors (Spatial dependence) The natural history of disease

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 TOC

To study disease, we need measures of its occurrence. • Some measures of disease occurrence • Counts • Prevalence • Incidence • Mortality Measures of disease occurrence

What are the health problems of the community? What are the attributes of these illnesses? DESCRIPTIVE Health and disease in the community What? Who? When? Where? 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 W’s needs to be defined carefully to get comparable measures across a province or state, a nation, the world. Epidemiologic approaches

Prevalence • 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.

Prevalence • 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.

1991 1995 2002 2006 No Data <10% 10%–14% 15%–19% 20%–24% ≥25% (*BMI ≥30, or ~ 30 lbs overweight for 5’ 4” woman) Obesity Trends Among U.S. Adults

Cases infected with the outbreak strain of SalmonellaSaintpaul, as of July 15, 2008 9 pm EDT. We would need to know the population in each state in order to determine the prevalence. Salmonella cases: Infected

If population size is 3.81 million, then The incidence of a disease is the rate at which new cases occur in a population during a specified period. Incidence

Incidence of cases of infection with the outbreak strain as of July 15, 2008 9pm EDT Salmonella cases: Incidence

Cases infected with the outbreak strain of SalmonellaSaintpaul, as of July 15, 2008 9pm EDT Cases and Incidence – Salmonella

Incidence and prevalence measure different aspects of disease occurrence PrevalenceIncidence Numerator: Denominator: Measures: Most useful: All cases, no matter how long diseased Only NEW cases All persons in pop Only persons at risk of disease Presence of disease Risk of disease Resource allocation Risk, etiology Incidence and Prevalence Etiology: the study of a disease’s causes.

Numerator • Number of deaths • Denominator • Number of individuals in population (how defined?) • Time interval • 1-year: Annual Mortality Rate • (typical to use an annual rate) • Specifier • age, sex, race, etc. Mortality Rate – Incidence of death

GIS and Health Geography