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The data consists of the cumulative 2012 West Nile Virus human cases from Center for Disease Control and Prevention. The numbers used were given to U.S. Geological Survey to put up on their Web site on May 14, 2013. The population data was taken from the 2012 population estimate from the U.S. Census.
The state incidence rate is the average incidence rate for that state and was calculated by adding all human cases for that particular state, dividing it by the population of that state and multiplying it by 10,000 people.
However, it’s important to note that these numbers may not represent the whole picture. The CDC’s West Nile Virus reporting system is a passive surveillance system, meaning it’s dependent on local clinicians testing, diagnosis and then sending their data to public health authorities.
The aggressiveness and efficiency of West Nile Virus case reporting and surveillance varies from county, state and region, sometimes vastly.
If the map shows a county with zero cases, it’s possible that there were no instances of West Nile Virus. However, it might also be that this particular county may not have a comprehensive surveillance system in place.
Even though West Nile Virus reporting is mandatory, the CDC does not keep track of the level of surveillance and case reporting for every county, metropolitan area and state.
In addition, West Nile Virus cases may go misdiagnosed due to many of the symptoms like high fevers overlapping with other illnesses. In particular, mild cases that don’t affect the nervous system often go undiagnosed.
That’s why incidences of West Nile Virus in the United States are underreported and incidence rates can be underestimated.
Consult your county health department to find out more specific information on how West Nile Virus cases are reported.
This map was created by the Patch Data Interactive team with John Ness as News Director.
Map Visualization: Carla Astudillo
Research and Writing: Heather Martino
Editing and Auto-localization: Martin Burch
Map Powered by Leaflet and CartoDB
Questions? Comments? Email us at data@patch.com