Eastern equine encephalitis virus (EEEV) is transmitted to humans through the bite of an infected mosquito. Human EEEV cases occur relatively infrequently, largely because the primary transmission cycle takes place in and around cedar or hardwood swamp areas where human populations tend to be limited. All residents of and visitors to areas where EEEV activity has been identified are at risk of infection. People who engage in outdoor work and recreational activities in endemic areas are at increased risk of infection. Persons over age 50 and under age 15 seem to be at greatest risk for developing severe disease when infected with EEEV. Overall, only about 4-5% of human EEEV infections result in EEE. EEEV infection is thought to confer life-long immunity against re-infection. It does not confer significant cross-immunity against other alphaviruses (e.g., western equine encephalitis virus), and it confers no cross-immunity against flaviviruses (e.g., West Nile virus) or bunyaviruses (e.g., La Crosse virus).

In the United States, an average of 11 human cases of EEE are reported annually. To ensure standardization of reporting across the country, CDC recommends that the national surveillance case definition be consistently applied by all state health departments.

From 2010-2019, most cases of EEE have been reported Massachusetts, Michigan, Florida, Georgia, New York, and North Carolina. EEEV transmission is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states and the Great Lakes region.

Eastern equine encephalitis virus neuroinvasive disease cases reported by year, 2010–2019* Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

*2019 data are provisional and subject to change Eastern equine encephalitis virus neuroinvasive disease cases reported by year, 2009–2018 Year Number of Reported Cases 2010 10 2011 4 2012 15 2013 8 2014 8 2015 6 2016 7 2017 5 2018 6 2019* 38 *2019 data are provisional and subject to change Print only version pdf icon[PDF – 1 page] Top of Page

Eastern equine encephalitis virus neuroinvasive disease cases reported by state of residence, 2010–2019* Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention *2019 data are provisional and subject to change Eastern equine encephalitis virus neuroinvasive disease cases reported by state of residence, 2009–2018 State Number of Reported Cases Alabama 2 Arkansas 1 Connecticut 5 Florida 13 Georgia 7 Indiana 1 Louisiana 1 Maine 2 Maryland 1 Massachusetts 22 Michigan 17 Missouri 1 Montana 1 New Hampshire 3 New Jersey 5 New York 7 North Carolina 7 Pennsylvania 1 Rhode Island 4 Tennessee 1 Vermont 2 Virginia 1 Wisconsin 2 *2019 data are provisional and subject to change Print only version pdf icon[PDF – 1 page] Top of Page

Eastern equine encephalitis virus neuroinvasive disease average annual incidence by county of residence, 2010–2019* Print only version pdf icon[PDF – 1 page] Data Table: This map shows the distribution of Eastern equine encephalitis virus neuroinvasive disease average annual incidence by county of residence from 2010 through 2019; 2019 data are provisional and subject to change. Counties are shaded according to incidences ranging from less than 0.20, 0.20 to 0.49, and greater than 0.50 per 100,000 population. Shaded counties are primarily distributed along the Gulf Coast, Eastern seaboard, and the Great Lakes. *2019 data are provisional and subject to change Top of Page

Additional Maps, Charts, and Tables

Eastern equine encephalitis virus disease cases and deaths reported to CDC by year and clinical presentation, 2010-2019*

Eastern equine encephalitis virus disease cases and deaths reported to CDC by year and clinical presentation, 2009-2018 Neuroinvasive disease Non-neuroinvasive disease Total Year Cases

No. Deaths

No. (%) Cases

No. Deaths

No. (%) Cases

No. Deaths

No. (%) 2010 10 5 (50) 0 0 (0) 10 5 (50) 2011 4 3 (75) 0 0 (0) 4 3 (75) 2012 15 5 (33) 0 0 (0) 15 5 (33) 2013 8 4 (50) 0 0 (0) 8 4 (50) 2014 8 2 (25) 0 0 (0) 8 2 (25) 2015 6 4 (67) 0 0 (0) 6 4 (67) 2016 7 3 (43) 0 0 (0) 7 3 (43) 2017 5 2 (40) 0 0 (0) 5 2 (40) 2018 6 1 (17) 0 0 (0) 6 1 (17) 2019* 38 19 (50) 0 0 (0) 38 19 (50) Total 107 48 (45) 0 0 (0) 107 48 (45)

*2019 data are provisional and subject to change

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Eastern equine encephalitis virus disease cases reported to CDC by state of residence, 2010-2019*

Eastern equine encephalitis virus disease cases reported to CDC by state of residence, 2009-2018 State 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019* Total Alabama 0 0 0 0 1 0 0 0 0 1 2 Alaska 0 0 0 0 0 0 0 0 0 0 0 Arizona 0 0 0 0 0 0 0 0 0 0 0 Arkansas 0 0 0 1 0 0 0 0 0 0 1 California 0 0 0 0 0 0 0 0 0 0 0 Colorado 0 0 0 0 0 0 0 0 0 0 0 Connecticut 0 0 0 1 0 0 0 0 0 4 5 Delaware 0 0 0 0 0 0 0 0 0 0 0 Dist. of Columbia 0 0 0 0 0 0 0 0 0 0 0 Florida 4 0 2 3 0 0 0 1 3 0 13 Georgia 0 0 1 1 0 0 1 2 1 1 7 Hawaii 0 0 0 0 0 0 0 0 0 0 0 Idaho 0 0 0 0 0 0 0 0 0 0 0 Illinois 0 0 0 0 0 0 0 0 0 0 0 Indiana 0 0 0 0 0 0 0 0 0 1 1 Iowa 0 0 0 0 0 0 0 0 0 0 0 Kansas 0 0 0 0 0 0 0 0 0 0 0 Kentucky 0 0 0 0 0 0 0 0 0 0 0 Louisiana 0 0 0 0 0 1 0 0 0 0 1 Maine 0 0 0 0 1 1 0 0 0 0 2 Maryland 0 0 0 0 0 0 0 1 0 0 1 Massachusetts 1 1 7 1 0 0 0 0 0 12 22 Michigan 3 0 0 0 1 0 2 0 1 10 17 Minnesota 0 0 0 0 0 0 0 0 0 0 0 Mississippi 0 0 0 0 0 0 0 0 0 0 0 Missouri 0 1 0 0 0 0 0 0 0 0 1 Montana 0 0 0 0 0 0 1 0 0 0 1 Nebraska 0 0 0 0 0 0 0 0 0 0 0 Nevada 0 0 0 0 0 0 0 0 0 0 0 New Hampshire 0 0 0 0 3 0 0 0 0 0 3 New Jersey 0 0 0 0 0 0 1 0 0 4 5 New Mexico 0 0 0 0 0 0 0 0 0 0 0 New York 1 1 0 0 2 3 0 0 0 0 7 North Carolina 0 0 2 1 0 1 2 0 0 1 7 North Dakota 0 0 0 0 0 0 0 0 0 0 0 Ohio 0 0 0 0 0 0 0 0 0 0 0 Oklahoma 0 0 0 0 0 0 0 0 0 0 0 Oregon 0 0 0 0 0 0 0 0 0 0 0 Pennsylvania 0 0 0 0 0 0 0 0 1 0 1 Puerto Rico 0 0 0 0 0 0 0 0 0 0 0 Rhode Island 1 0 0 0 0 0 0 0 0 3 4 South Carolina 0 0 0 0 0 0 0 0 0 0 0 South Dakota 0 0 0 0 0 0 0 0 0 0 0 Tennessee 0 0 0 0 0 0 0 0 0 1 1 Texas 0 0 0 0 0 0 0 0 0 0 0 Utah 0 0 0 0 0 0 0 0 0 0 0 Vermont 0 0 2 0 0 0 0 0 0 0 2 Virginia 0 0 1 0 0 0 0 0 0 0 1 Washington 0 0 0 0 0 0 0 0 0 0 0 West Virginia 0 0 0 0 0 0 0 0 0 0 0 Wisconsin 0 1 0 0 0 0 0 1 0 0 2 Wyoming 0 0 0 0 0 0 0 0 0 0 0 Total 10 4 15 8 8 6 7 5 6 38 107

*2019 data are provisional and subject to change

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