Epidemiology & Geographic Distribution

In the United States, an average of 65 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 (Ohio, Wisconsin, Minnesota, Indiana, Iowa, and Illinois). Recently, more cases have been reported from mid-Atlantic and southeastern states (North Carolina, Tennessee, West Virginia, Georgia, Virginia, and Kentucky).

La Crosse virus neuroinvasive disease cases reported by year, 2008–2017

A line chart depicting La Crosse encephalitis cases by year starting from 2008 to 2017.

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

La Crosse virus neuroinvasive disease cases reported by year, 2007–2016
Year	Number of Reported Cases
2008	49
2009	44
2010	67
2011	116
2012	71
2013	77
2014	76
2015	51
2016	31
2017	63

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Data Table: In the United States, the number of La Crosse virus neuroinvasive disease cases reported each year varies. From 2008 through 2017, an average of 65 cases were reported annually (range 31–116).

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La Crosse virus neuroinvasive disease cases reported by state of residence, 2008–2017

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

La Crosse virus neuroinvasive disease cases reported by state of residence, 2008–2017
State	Number of Reported Cases
Alabama	2
Florida	2
Georgia	14
Illinois	1
Indiana	6
Iowa	1
Kansas	1
Kentucky	2
Louisiana	2
Maryland	3
Michigan	3
Minnesota	19
Mississippi	4
Missouri	1
North Carolina	175
Ohio	179
South Carolina	4
Tennessee	101
Texas	4
Virginia	8
West Virginia	86
Wisconsin	27

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Data table: From 2008 through 2017, La Crosse virus neuroinvasive disease cases have been reported in Alabama (2), Florida (2), Georgia (14), Illinois (1), Indiana (6), Iowa (1), Kansas (1), Kentucky (2), Louisiana (2), Maryland (3), Michigan (3), Minnesota (19), Mississippi (4), Missouri (1), North Carolina (175), Ohio (179), South Carolina (4), Tennessee (101), Texas (4), Virginia (8), West Virginia (86) and Wisconsin (27).

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La Crosse virus neuroinvasive disease average annual incidence by county of residence, 2008–2017

A map of the continental United States depicting California Serogroup Virus Neuroinvasive Disease Average Annual Incidence by County, 2008 to 2017.

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 2008 through 2017. 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, 2008-2017

La Crosse virus disease cases and deaths reported to CDC by year and clinical presentation, 2008-2017
	Neuroinvasive disease		Non-neuroinvasive disease		Total
Year	Cases No.	Deaths No. (%)	Cases No.	Deaths No. (%)	Cases No.	Deaths No. (%)
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)
2017	63	0 (0)	0	0 (0)	63	0 (0)
Total	645	9 (1)	58	0 (0)	703	9 (<1)

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La Crosse virus disease cases reported to CDC by state of residence, 2008–2017

La Crosse virus disease cases reported to CDC by state of residence and year, 2008–2017
State	2008	2009	2010	2011	2012	2013	2014	2015	2016	2017	Total
Alabama	0	0	0	1	0	1	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	1	0	0	0	3
Georgia	2	2	2	2	0	1	2	2	0	2	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	0	1	0	0	0	0	0	0	0	1	2
Indiana	0	1	0	2	3	1	0	0	0	0	7
Iowa	0	0	0	0	0	0	0	0	0	1	1
Kansas	0	0	0	0	0	0	0	1	0	0	1
Kentucky	1	0	0	1	0	0	0	0	0	0	2
Louisiana	1	0	0	0	0	0	0	1	0	0	2
Maine	0	0	0	0	0	0	0	0	0	0	0
Maryland	0	0	2	0	0	0	0	0	0	1	3
Massachusetts	0	0	0	0	0	0	0	0	0	0	0
Michigan	0	0	2	1	0	0	0	0	0	0	3
Minnesota	1	0	1	1	4	5	4	1	3	1	21
Mississippi	3	0	0	0	1	3	0	0	0	0	7
Missouri	0	1	0	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	1	0	0	0	0	0	0	0	1
North Carolina	9	16	22	26	26	13	23	11	8	21	175
North Dakota	0	0	0	0	0	0	0	0	0	0	0
Ohio	9	5	24	50	13	16	31	24	9	13	194
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	1	1	1	0	1	0	0	4
South Dakota	0	0	0	0	0	0	0	0	0	0	0
Tennessee	6	8	11	12	9	23	11	4	3	17	104
Texas	0	0	1	0	3	0	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	2	1	0	1	2	2	2	0	0	0	10
Washington	0	0	0	0	0	0	0	0	0	0	0
West Virginia	14	14	8	26	14	11	2	4	8	4	105
Wisconsin	4	1	0	5	2	8	4	6	4	2	36
Wyoming	0	0	0	0	0	0	0	0	0	0	0
Total	53	50	74	130	78	85	80	55	35	63	703