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Epidemiology & Geographic Distribution

In the United States, an average of 63 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. 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 (Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio). Recently, more cases have been reported from mid-Atlantic and southeastern states (West Virginia, Virginia, Kentucky, North Carolina, and Tennessee).

La Crosse virus neuroinvasive disease cases reported by year, 2007–2016

A line chart depicting La Crosse encephalitis cases by year starting from 2007 to 2016.

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

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Data Table: In the United States, the number of La Crosse virus neuroinvasive disease cases reported each year varies. From 2007 through 2016, an average of 63 cases were reported annually (range 31–116).

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La Crosse virus neuroinvasive disease cases reported by state of residence, 2007–2016

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Cases reported by state, 2007 to 2016.

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

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Data table: From 2007 through 2016, La Crosse virus neuroinvasive disease cases have been reported in Alabama (2), Florida (2), Georgia (13), Indiana (6), Illinois (1), Iowa (1), Kansas (1), Kentucky (2), Louisiana (2), Maryland (2), Michigan (3), Minnesota (19), Mississippi (4), Missouri (1), North Carolina (163), Ohio (175), South Carolina (4), Tennessee (97), Texas (4), Virginia (8), West Virginia (93) and Wisconsin (27).

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La Crosse virus neuroinvasive disease average annual incidence by county of residence, 2007–2016

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Average Annual Incidence by County, 2007 to 2016.
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 of residence from 2007 through 2016. 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.

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Additional Maps, Charts, and Tables

La Crosse virus disease cases and deaths reported to CDC by year and clinical presentation, 2007-2016

Neuroinvasive disease Non-neuroinvasive disease Total
Year Cases
No.		 Deaths
No. (%)		 Cases
No.		 Deaths
No. (%)		 Cases
No.		 Deaths
No. (%)
2007 48 1  (2) 5 0  (0) 53 1  (2)
2008  49 0  (0) 4 0  (0) 53 0  (0)
2009 44 1  (2) 6 0  (0) 50 1  (2)
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)
Total 630 10  (2)  63 0  (0) 693 10  (1) 

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La Crosse virus disease cases reported to CDC by state of residence and year, 2007–2016

State 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total
Alabama 0 0 0 0 1 0 1 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 1 0 0 3
Georgia 2 2 2 2 2 0 1 2 2 0 15
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 1 0 1 0 0 0 0 0 0 0 2
Indiana 0 0 1 0 2 3 1 0 0 0 7
Iowa 1 0 0 0 0 0 0 0 0 0 1
Kansas 0 0 0 0 0 0 0 0 1 0 1
Kentucky 0 1 0 0 1 0 0 0 0 0 2
Louisiana 0 1 0 0 0 0 0 0 1 0 2
Maine 0 0 0 0 0 0 0 0 0 0 0
Maryland 0 0 0 2 0 0 0 0 0 0 2
Massachusetts 0 0 0 0 0 0 0 0 0 0 0
Michigan 0 0 0 2 1 0 0 0 0 0 3
Minnesota 1 1 0 1 1 4 5 4 1 3 21
Mississippi 0 3 0 0 0 1 3 0 0 0 7
Missouri 0 0 1 0 0 0 0 0 0 0 1
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 1 0 0 0 0 0 0 1
North Carolina 10 9 16 22 26 26 13 23 11 8 164
North Dakota 0 0 0 0 0 0 0 0 0 0 0
Ohio 9 9 5 24 50 13 16 31 24 9 190
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 0 0 0
South Carolina 0 0 0 0 1 1 1 0 1 0 4
South Dakota 0 0 0 0 0 0 0 0 0 0 0
Tennessee 14 6 8 11 12 9 23 11 4 3 101
Texas 0 0 0 1 0 3 0 0 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 0 2 1 0 1 2 2 2 0 0 10
Washington 0 0 0 0 0 0 0 0 0 0 0
West Virginia 11 14 14 8 26 14 11 2 4 8 112
Wisconsin 4 4 1 0 5 2 8 4 6 4 38
Wyoming 0 0 0 0 0 0 0 0 0 0 0
Total 53 53 50 74 130 78 85 80 55 35 693

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