Epidemiology & Geographic Distribution

In the United States, an average of 68 La Crosse encephalitis virus (LACV) neuroinvasive disease cases are reported each year. There is significant under-diagnosis and under-reporting of less severe cases of LACV disease, therefore reported LACV neuroinvasive disease cases are used to compare trends over time and place. LACV disease is a nationally notifiable condition. To ensure standardization of reporting across the country, CDC recommends that the national surveillance case definition (standardized reporting criteria) be consistently applied by all state health departments.

LACV disease cases occur primarily from late spring through early fall, but in subtropical endemic areas (e.g., the Gulf states), rare cases can occur in winter. Historically, most cases of LACV neuroinvasive disease were reported from the upper Midwestern states (Ohio, Wisconsin, Minnesota, Indiana, Iowa, and Illinois). Recently, more cases have been reported from northeastern, mid-Atlantic and southeastern states (Rhode Island, North Carolina, Tennessee, West Virginia, Georgia, Virginia, and Kentucky).

La Crosse virus neuroinvasive disease cases reported by year, 2010–2019*

A line chart depicting La Crosse encephalitis cases by year starting from 2009 to 2018.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention
*2019 data are provisional and subject to change

La Crosse virus neuroinvasive disease cases reported by year, 2007–2016
Year Number of Reported Cases
2010 67
2011 116
2012 71
2013 77
2014 76
2015 51
2016 31
2017 63
2018 83
2019* 46

*2019 data are provisional and subject to change

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La Crosse virus neuroinvasive disease cases reported by state of residence, 2010–2019*

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Cases reported by state, 2008 to 2017.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention
*2019 data are provisional and subject to change

La Crosse virus neuroinvasive disease cases reported by state of residence, 2008–2017
State Number of Reported Cases
Alabama 2
Florida 2
Georgia 11
Illinois 1
Indiana 5
Iowa 1
Kansas 1
Kentucky 2
Louisiana 1
Maryland 3
Michigan 4
Minnesota 18
Mississippi 3
North Carolina 179
Ohio 222
Rhode Island 2
South Carolina 4
Tennessee 111
Texas 5
Virginia 8
West Virginia 70
Wisconsin 26

*2019 data are provisional and subject to change

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La Crosse virus neuroinvasive disease average annual incidence by county of residence, 2010–2019*

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Average Annual Incidence by County, 2009 to 2018.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention
*2019 data are provisional and subject to change

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Data table: This map shows the distribution of La Crosse virus neuroinvasive disease (encephalitis and/or meningitis) average annual incidence by county from 2010 through 2019. Counties are shaded according to incidences ranging from less than 1.00, 1.00 to 2.49, and greater than 2.50 per 100,000 population. Shaded counties are primarily distributed in eastern half of the country. Most of the highest incidence counties are along the Appalachian range and central Ohio.

*2019 data are provisional and subject to change

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Additional Maps, Charts, and Tables

La Crosse virus disease cases and deaths reported to CDC by year and clinical presentation, 2010-2019*

La Crosse 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 67 1  (1) 7 0  (0) 74 1  (1)
2011 116 1  (1) 14 0  (0) 130 1  (1)
2012 71 1  (1) 7 0  (0) 78 1  (1)
2013 77 2  (3) 8 0  (0) 85 2  (2)
2014 76 3  (4) 4 0  (0) 80 3  (4)
2015 51 0  (0) 4 0  (0) 55 0  (0)
2016 31 0  (0) 4 0  (0) 35 0  (0)
2017 63 0  (0) 0 0  (0) 63 0  (0)
2018 83 0  (0) 3 0  (0) 86 0  (0)
2019* 46 0  (0) 7 0  (0) 53 0  (0)
Total 681 8  (1) 58 0  (0) 739 8 (1)

*2019 data are provisional and subject to change

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La Crosse virus disease cases reported to CDC by state of residence, 2010–2019*

La Crosse virus disease cases reported to CDC by state of residence and year, 2009–2018
State 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019* Total
Alabama 0 1 0 1 0 0 0 0 0 0 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 0 0 0 0 0 0 0 0
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 0 0 0 0 0 0 0 0
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 0 1 0 0 1 0 0 0 0 0 2
Georgia 2 2 0 1 2 2 0 2 0 1 12
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 1 0 0 1
Indiana 0 2 3 1 0 0 0 0 0 0 6
Iowa 0 0 0 0 0 0 0 1 0 0 1
Kansas 0 0 0 0 0 1 0 0 0 0 1
Kentucky 0 1 0 0 0 0 0 0 0 1 2
Louisiana 0 0 0 0 0 1 0 0 0 0 1
Maine 0 0 0 0 0 0 0 0 0 0 0
Maryland 2 0 0 0 0 0 0 1 0 0 3
Massachusetts 0 0 0 0 0 0 0 0 0 0 0
Michigan 2 1 0 0 0 0 0 0 0 1 4
Minnesota 1 1 4 5 4 1 3 1 0 0 20
Mississippi 0 0 1 3 0 0 0 0 0 0 4
Missouri 0 0 0 0 0 0 0 0 0 0 0
Montana 0 0 0 0 0 0 0 0 0 0 0
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 0 0 0 0 0 0 0
New Jersey 0 0 0 0 0 0 0 0 0 0 0
New Mexico 0 0 0 0 0 0 0 0 0 0 0
New York 1 0 0 0 0 0 0 0 0 0 1
North Carolina 22 26 26 13 23 11 8 21 24 5 179
North Dakota 0 0 0 0 0 0 0 0 0 0 0
Ohio 24 50 13 16 31 24 9 13 39 26 245
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 0 0 0
Puerto Rico 0 0 0 0 0 0 0 0 0 0 0
Rhode Island 0 0 0 0 0 0 0 0 1 1 2
South Carolina 0 1 1 1 0 1 0 0 0 0 4
South Dakota 0 0 0 0 0 0 0 0 0 0 0
Tennessee 11 12 9 23 11 4 3 17 13 12 115
Texas 1 0 3 0 0 0 0 0 1 0 5
Utah 0 0 0 0 0 0 0 0 0 0 0
Vermont 0 0 0 0 0 0 0 0 0 0 0
Virginia 0 1 2 2 2 0 0 0 2 0 9
Washington 0 0 0 0 0 0 0 0 0 0 0
West Virginia 8 26 14 11 2 4 8 4 6 3 86
Wisconsin 0 5 2 8 4 6 4 2 0 3 34
Wyoming 0 0 0 0 0 0 0 0 0 0 0
Total 74 130 78 85 80 55 35 63 86 53 739

*2019 data are provisional and subject to change

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