Putting health on the map
In 2002, Cook County, Ill., had the highest number of West Nile virus cases in the country. Residents reported 299 cases of the virus, including 17 fatalities. The high incidence rate was unusual, particularly because the county did not see any cases of the virus in 2001.
The county public health department began receiving reports of dead birds in late spring, and by early August, the department was using a geographic information system (GIS) to track the outbreak by mapping cases of people who had contracted the virus. As new cases emerged, the department plotted their locations in a GIS and delineated buffer zones around them. The department shared the maps with mosquito abatement districts that targeted mosquito-spraying efforts where they were most needed.
Like Cook County, local public health agencies across the country are placing greater emphasis on disease surveillance, preparedness and response coordination to combat health threats such as West Nile virus, anthrax, Severe Acute Respiratory Syndrome (SARS) and bioterrorism. They are finding that GIS is an effective technology for aggregating, integrating and displaying data from various sources to create complete pictures of health conditions in their jurisdictions. GIS allows public health practitioners to put their data on a map, where they can easily assess patterns, trends and relationships between health events and environmental, socio-economic and geographic factors.
“GIS is an extremely powerful tool for local public health practice,” says Patrick Libbey, executive director for the Washington, D.C.-based National Association of County and City Health Officials. “The connection of GIS technology with the core sciences of public health provides an extraordinary means to better understand and communicate the dynamics of health conditions at the community level.”
GIS mapping and analysis capabilities can assist virtually all public health functions by combining data sets such as disease reports, demographics, health care facility usage and vital records with geographic data layers (i.e., census tracts, towns, counties, land use, facility locations). As a result, public health agencies can better monitor environmental health, track community health and plan programs targeted to specific areas of the community.
Monitoring the environment
Because environmental health programs rely heavily on information about the land, GIS has helped many health departments keep track of a variety of inspections. For example, the Florida Department of Health, Division of Environmental Health, has used GIS to create Internet maps for the Florida Healthy Beaches Program. The program uses state and federal funding to monitor 305 beach locations in 34 coastal counties weekly for the bacterial indicators enterococcus and fecal coliform. While those bacteria may not necessarily be pathogenic, they are useful indicators of potential fecal contamination. If waste pathogens are present in high concentrations in recreational waters and are ingested while swimming or enter the skin through a cut or sore, they may cause gastrointestinal illness, infections or rashes.
Beginning in 2000, staff members at the 34 coastal county health departments used global positioning system (GPS) units to precisely record locations of beach water sampling points. Then Environmental Health personnel use GIS software to create maps depicting the sampling points and other reference layers (e.g. roads).
The county health departments collect weekly samples and submit them to a database through an online entry site. The weekly sampling results are tracked with the database and presented with the maps online. The Web page is updated automatically when counties submit new information.
“The use of GIS helps us to go back to the same piece of water off the beach every week — even if it is a different county field inspector from one week to the next,” says Chris DuClos, GIS/GPS manager for the division. “The GIS maps give the public a geographic reference, so they can understand where these beaches are in relation to their homes, hotels, etc. In the future, we want to make the Internet maps dynamic so that they can zoom in and see minor roads and canal outfalls.”
To expand the use of GIS in local environmental health departments, last year Florida issued all county health departments GIS software and trained county personnel to use it. The state has a central GIS to collect information about inspections for drinking water wells, tanning salons and public swimming pools. Like the beach quality program, local inspectors collect data for the central GIS, but they also create their own maps for local projects. “The only way to track where things occur and associate them with environmental conditions with any degree of accuracy is to use GIS and GPS,” DuClos says. “It’s just a really good tool for us to track things through time and draw associations between what we see occurring and human health patterns.”
Tracking diseases
By connecting health records to specific addresses, census tracts, zip codes or counties, GIS can be used to pinpoint concentrations of disease, track the spread of disease and contribute to risk assessment and public notification. The Cook County Department of Public Health (CCDPH) was an early adopter of GIS technology and began using it in the early 1990s to map AIDS case rates for jurisdictions. The department began creating maps that showed the distribution of the disease throughout the suburban area. “Certain diseases are required by law to be reported by physicians to the local health department,” says Steven Seweryn, director of epidemiology for CCDPH. “Part of our duty as a public health department is to summarize that data and provide some feedback to reporting sources, as well as just know what the status of diseases are in our area.”
Similarly, the Communicable Disease Control Division of the Boston Public Health Commission (BPHC) is using GIS to monitor and analyze public health throughout Boston. “We use GIS to look at the spatial pattern of occurrence of water-borne illnesses, such as giardia, throughout the city,” says Scott Troppy, epidemiologist at BPHC. “By geocoding the water-borne illness cases to specific locations, we are able to maintain a picture of where and whether events are concentrated, which helps to guide our response or investigation.”
Nearby, on Cape Cod, GIS has been used to investigate the higher-than-state-average incidence of breast cancer. In a study funded by the Massachusetts Department of Public Health, the Newton, Mass.-based Silent Spring Institute has been examining the relationships of 2,100 individual women to multiple environmental pollutants over the past 40 years. GIS has allowed epidemiologists to bring potential exposure to environmental factors into focus by analyzing public and private water supplies, public sewers and septic systems, the 40-year residential history of 2,500 women, and land use going back 50 years.
The Institute gathered parcel data from each of the 15 towns on the Cape. Proximity analysis tools were created that account for prevailing winds and the effects of intervening vegetation to calculate residential exposure to drift from aerial pesticides used on cranberry bogs. Epidemiologists have been able to use those tools to determine how far breast cancer patients lived from cranberry bogs and whether they would have been exposed to pesticides that drifted during aerial application.
Planning services
The ability of GIS to combine health provider data with regional demographic data allows users to calculate service areas or markets, helps to identify underserved populations, and can help public health agencies efficiently allocate scarce program resources to appropriate locations. For example, BPHC uses GIS to help identify at-risk populations and determine where to focus efforts to vaccinate residents against influenza.
The department is mapping the locations of its health infrastructure, such as hospitals and community health centers, and identifying how close facilities are to elderly, disabled, non-native English speakers and low-income population groups. “We also take into account public transportation, and, by combining the various factors, we are able to identify which census tracts have higher proportions of at-risk populations in combination with their level of access to health resources by type,” Troppy says. “This information helps us to plan for the use of additional sites — libraries or schools — for the delivery of flu shots during a pandemic, for example, or for potential shelters for emergency situations.”
BPHC also maintains a Web-based dynamic map of 11 emergency departments (ED) and urgent care (UC) centers. The map is integrated with an existing Web-based utilization status surveillance system, and it displays whether ED and UC usage (number of visits) exceeds an expected threshold level set by the BPHC. Such a pattern may serve as an early indicator of bioterrorism or another public health concern. The map automatically updates to show daily utilization status, and users can scroll to prior dates.
In 1998, GIS played a supporting role during CCDPH’s recertification process, in which the department presented data about health indicators to community representatives. Because the department had to present data about 129 communities, health indicator maps helped the county show communicable disease case rates and leading causes of death by communities.
The department’s presentation was used to identify priorities for health services. “Maps are certainly more interesting to look at than tables and graphs, and they’re more easily understood by people who receive the data,” Seweryn says. “The use of maps helps present data for 129 communities in a straightforward, easy-to-understand manner, where you can visualize and identify problem areas very quickly.”
Expanding capabilities
The barriers to GIS application in public health are falling. Health departments can take advantage of investments made by states, cities and counties throughout the nation in GIS data development.
Local health departments in North Carolina, for example, soon will have more capacity to use GIS. The North Carolina Center for Geographic Information & Analysis, the Duke University Children’s Environmental Health Initiative, and the North Carolina Department of Health and Human Resources are cooperating under a grant from the Centers for Disease Control to build capacity for GIS technology in local health departments. The project is beginning with health departments in Craven, New Hanover, Pamlico, and Wayne counties and the Albemarle Regional Health Services, which represents five additional counties in eastern North Carolina.
The agencies are working together to procure and install hardware and software, develop GIS applications and train county health department personnel in the use of GIS and database tools. Participating health departments are using GIS to support a variety of applications in environmental health, including septic tank inspections, mosquito spraying programs, restaurant inspections, well sampling and potential water contamination sources. Counties now are planning public health applications of GIS for the analysis of sexually transmitted diseases, asthma, lead poisoning and other infectious diseases.
Not all data sets or records can be explicitly mapped or made available to the public, but data can be aggregated to census tracts or combinations of census tracts to show a picture that the public and other community officials can understand. “GIS is a natural for public health,” Troppy says. “When public health officials see their data on a map, they immediately recognize the value of the technology.”
Joan Gardner is chairman and treasurer, and Thomas Harrington is director of marketing for Applied Geographics, which is based in Boston.
