Mapping HIV Incidence in North Carolina

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Mapping HIV Incidence in North Carolina

• Exploratory Analysis of Disease Data
• Introduction to UNCs GIS Reference Library
• Prepared by Kristen Hampton
• for ENVR 167
• October 4, 2004

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Disclaimer

• All disease data introduced in this presentation
  is fictional, for demonstration purposes only,
  and should not be considered valid or used for
  any type of research publication.

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Types of Investigations

• Disease mapping
• Summation of spatial and spatio-temporal
  variation in disease risk
• Geographical Correlation Analysis
• Relationship between heath outcomes and
  environmental risk factors
• Disease clustering
• Raised incidence of disease in an area
• Non-random spatial pattern of disease relative to
  non-cases

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Disease Mapping
(Zucker, J.R. Changing Patterns of Autochthonous
Malaria Transmission in the United States A
Review of Recent Outbreaks. Emerging Infectious
Diseases. 19962(1)37-43.)
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Geographical Correlation Analysis
(Glass, G.E. et al. Infectious Disease
Epidemiology and GIS A Case Study of Lyme
Disease. Geo Info Systems. 19922(10)65-69.)
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Disease ClusteringGCA Point Source Study
John Snows 1854 Map of Cholera and the Broad
Street Pump

• Hypothesis of disease etiology
• Layers
• Roads
• Pumps
• Case event data

(McLeod, K.S. Our sense of Snow the myth of John
Snow in medical geography. Social Science
Medicine. 200050923-935.)
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ID Application of GIS

• Continuum of diseases
• Highly applicable to environmental diseases,
  such as malaria and other vector-borne diseases
• Limited applicability to non-communicable
  diseases, such as MS, with weak or non-existent
  environmental components
• In between are HIV and other STDs with moderately
  strong links to the environment

(Tanser, F.C. et al. The application of
geographical information systems to important
public health problems in Africa. Int. J Health
Geographics. 200214.)
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I-95 Syphilis Study
(Cook et al. Whats driving an epidemic? The
Spread of Syphilis Along an Interstate Highway in
Rural North Carolina. Am. J of Public Health.
1999 Mar89(3)369-373.)
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I-95 Syphilis Study
(Cook et al. Whats driving an epidemic? The
Spread of Syphilis Along an Interstate Highway in
Rural North Carolina. Am. J of Public Health.
1999 Mar89(3)369-373.)
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Issues

• Confounding
• Resolution / Aggregation level
• Patient confidentiality
• Spatial accuracy
• Ecological Fallacy (individual v. group)
• Temporal relationship between exposure and
  disease

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Exploratory Analysis of HIV Incidence in NC

• Screening and Tracing for Acute HIV Transmission
  (STAT)
• Collaboration between UNC-CH CFAR and NC DHHS
• Developed a system using HIV biomarkers to
  determine the time of transmission (incident
  cases)
• All HIV test samples sent to state labs are
  staged with the STAT protocol
• Records are mapped according to self-reported zip
  code of residence
• Between 11/1/02 and 5/31/04
• 164,836 mappable records
• 888 prevalent cases
• 217 incident cases

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Goal

• Given a table of patient records with disease X
  in North Carolina, create choropleth maps of
• i. case count,
• ii. density of cases per square mile, and
• iii. population density (persons per square
  mile)
• by zip code, shown with major highways.

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Road Classification
Major Highway
No. of Cases
0
1
2
3
4 - 9
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Information Needed

• Tabular Data (Given)
• .dbf (dbase) or .txt (text) file formats
• GIS Data
• Polygon shapefile of NC zip codes
• Line shapefile of NC roads
• Attribute Data
• Zip code area and population

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Resources

• http//www.lib.unc.edu/reference/gis/
• Amanda Henley
• GIS Reference Librarian, Davis Library
• ahenley_at_refstaff.lib.unc.edu
• ArcGIS desktop Help

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Exercise

• Handout
• Searching UNCs GIS Database
• Additional Exercises
• Adding X,Y Coordinates of Polygon Centroids
• Creating Raster Density Maps from Point Layers
• Geocoding a Table of Addresses