Statistics & Maps

LAC virus disease is a nationally notifiable condition. Cases are reported to CDC by state and local health departments using the national surveillance case definition. 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.

In the United States, 50-150 La Crosse encephalitis (LAC) virus neuroinvasive disease cases are reported each year. There is substantial under-diagnosis and under-reporting of less severe cases of LAC disease; therefore, reported LAC neuroinvasive disease cases are used to compare trends over time and place.

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

Anyone in an area where LAC virus is circulating can get infected with the virus. The risk is highest for people who live, work, or recreate in woodland habitats, because of greater exposure to potentially infected mosquitoes.

La Crosse virus neuroinvasive disease cases reported by year, 2011–2020

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

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La Crosse virus neuroinvasive disease cases reported by year, 2007–2016
Year Number of Reported Cases
2011 116
2012 71
2013 77
2014 76
2015 51
2016 31
2017 63
2018 83
2019 48
2020 84

La Crosse virus neuroinvasive disease cases reported by state of residence, 2011–2020

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Cases reported by state, 2011 to 2020.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

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La Crosse virus neuroinvasive disease cases reported by state of residence, 2008–2017
State Number of Reported Cases
Alabama 2
Florida 2
Georgia 10
Illinois 2
Indiana 6
Iowa 1
Kansas 1
Kentucky 7
Louisiana 1
Maryland 1
Michigan 2
Minnesota 18
Mississippi 3
North Carolina 179
Ohio 232
Rhode Island 2
South Carolina 5
Tennessee 117
Texas 4
Virginia 9
West Virginia 68
Wisconsin 28

La Crosse virus neuroinvasive disease average annual incidence by county of residence, 2011–2020

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Average Annual Incidence by County, 2011 to 2020.

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

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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 2011 through 2020. 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.

Additional Maps, Charts, and Tables

La Crosse virus disease cases and deaths reported to CDC by year and clinical presentation, 2011-2020

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. (%)
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 48 0  (0) 7 0  (0) 55 0  (0)
2020 84 0  (0) 4 0  (0) 88 0  (0)
Total 700 7  (1) 55 0  (0) 755 7 (1)

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

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La Crosse virus disease cases reported to CDC by state of residence, 2011–2020

La Crosse virus disease cases reported to CDC by state of residence and year, 2009–2018
State 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Total
Alabama 1 0 1 0 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 1 0 0 1 0 0 0 0 0 0 2
Georgia 2 0 1 2 2 0 2 0 1 1 11
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 1 0 0 1 2
Indiana 2 3 1 0 0 0 0 0 0 1 7
Iowa 0 0 0 0 0 0 1 0 0 0 1
Kansas 0 0 0 0 1 0 0 0 0 0 1
Kentucky 1 0 0 0 0 0 0 0 1 5 7
Louisiana 0 0 0 0 1 0 0 0 0 0 1
Maine 0 0 0 0 0 0 0 0 0 0 0
Maryland 0 0 0 0 0 0 1 0 0 0 1
Massachusetts 0 0 0 0 0 0 0 0 0 0 0
Michigan 1 0 0 0 0 0 0 0 1 0 2
Minnesota 1 4 5 4 1 3 1 0 1 0 20
Mississippi 0 1 3 0 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 0 0 0 0 0 0 0 0 0 0 0
North Carolina 26 26 13 23 11 8 21 24 6 21 179
North Dakota 0 0 0 0 0 0 0 0 0 0 0
Ohio 50 13 16 31 24 9 13 39 26 33 254
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 1 1 0 2
South Carolina 1 1 1 0 1 0 0 0 0 1 5
South Dakota 0 0 0 0 0 0 0 0 0 0 0
Tennessee 12 9 23 11 4 3 17 13 12 15 119
Texas 0 3 0 0 0 0 0 1 0 0 4
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 1 2 2 2 0 0 0 2 0 1 10
Washington 0 0 0 0 0 0 0 0 0 0 0
West Virginia 26 14 11 2 4 8 4 6 3 7 85
Wisconsin 5 2 8 4 6 4 2 0 3 2 36
Wyoming 0 0 0 0 0 0 0 0 0 0 0
Total 130 78 85 80 55 35 63 86 55 88 755

Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention

To request data for previous years, please email dvbid2@cdc.gov.

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