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John Bizelli - jbizellialeegov . com <br /> Amy Hoyf - hoytalCaleegov .com <br /> Courtney Sullivan - csullivanC�sullivan-ward . net <br /> Case Study courtesy of Lee County Human Services Department <br /> Epidemiology and GIS Prince William County Virginia Health Department <br /> 17. lip <br /> Epidemiology researchers can find clues to the spread of a disease as they study outbreaks <br /> of the disease through time, location , and groupings of people . In many cases , people with <br /> an illness belong to several groups such as family , school , church , and work . These groups <br /> are also identified by location . By mapping the location of various groups and looking at the <br /> presence of illness over time, it may be easier to identify the source of a disease and how it <br /> spreads . Knowing these factors can help doctors create a plan to halt the spread of disease . <br /> The maps shown here depict the spread of measles through Prince William County in 1988 . <br /> The locations of the patients by home address show a random pattern , while the plot by <br /> school shows obvious aggregations of cases . When viewed by two-week periods, the spread <br /> of the illness from school to school becomes apparent . In fact, during the outbreak it was <br /> possible to document dating patterns and sporting events that facilitated this spread . One of <br /> the control measures was halting certain sporting events . <br /> Using additional GIS data layers , researchers can look for possible links to diseases by <br /> comparing disease clusters with extremely hazardous substance site ( EHS ) facilities and their <br /> vulnerability zones . In cases of illness for gastroenteritis , clusters can be viewed and possibly <br /> identified with restaurants and other commonly frequented establishments. <br /> By implementing this analytical process with GIS , epidemiologists can identify, locate , and <br /> group illnesses with people, places , and activities; develop a plan ; and initiate control <br /> measures to halt the spread of disease . This kind of process was used in handling the <br /> potential threat of the West Nile virus and the outbreak of human encephalitis , which began <br /> in New York City in early August 1999 . <br /> 'Case Study Courtesy of ESRI Map Book Gallery Volume 16 <br /> 224 <br /> GIS Needs Assessment and Implementation Plan Chapter I - Departmental GIS Needs Assessment <br />