cases that had occurred since 1992 were plotted out, address matched and placed over the base map. Hoffman noted that all of the subsequent cases were located in the same areas that had high infection rates during the 1989-1991 outbreak. "Most of the cases occurred where we predicted; none occurred in low-risk areas. The characteristics that best predicted the number of measles cases were race and ethnicity (a positive association for Hispanics living within a 1990 Census tract); income level (positive for lower, negative for higher); age (positive for younger, negative for some middle-age groups); marital status (positive for divorced men and women and for single-parent families); and births (positive for the number of births)."
The project concluded with a presentation to the Department of Public Health, along with delivery of the ArcView application, maps and charts with descriptive epidemiology, and the software tools needed to conduct further analysis.
Although much of the information provided by the study was already known to the department, Prendergast said the more sophisticated methods of GIS analysis revealed some interesting insights into the county's populations, particularly where the risks of measles were high. "It showed that in the white population of the county, where there are small areas characterized by low economic status and high-density housing, there was a higher measles rate than occurred in other places. That's a relatively small insight, but a significant one for us to have gained by the analysis, and one we would not otherwise have easily known. The study was well worth the effort. It produced incredible visual aids to show how an epidemic affects places."
The study also had economic benefits. As Tracy pointed out, the database provided by the research will be used in conjunction with the department's automated immunization registry, which currently maintains records of 68,000 children and supports reminder activities for about 198,000. Merging current immunization records with the research data will enable the department to plan vaccine coverage based on population and birth data. "The fact that those records are automated with address detail," Tracy said, "provides a powerful tool for current policy and planning, and up-to-date analysis in the event of an outbreak." Tracy added that it was the cooperative efforts of the department, Loma Linda School of Public Health and ESRI that enabled them to have the database for this application at modest cost.
As the planet continues to shrink in size while increasing in population -- doubling to more than 11 billion in the next 45 years -- GIS technology, and the cooperative efforts between education, government and the private sector, will continue to play an important role in the battle against infectious diseases.
Epi Info (CDC, Atlanta)