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Human Powassan (POW) virus infections have been recognized in the United States, Canada and Russia. In the United States, cases of POW virus disease have been reported primarily from northeastern states and the Great Lakes region. These cases occur primarily in the late spring, early summer and mid-fall when ticks are most active.

POW virus disease is a nationally notifiable condition. Cases are reported to CDC by state and local health departments using standard case definitions. POW virus disease cases are rare but the reported number of cases have increased in recent years.

All residents of and visitors to areas where POW virus 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.

Powassan virus neuroinvasive disease cases reported by year, 2009–2018

Graph showing Powassan virus neuroinvasive disease cases reported by year, 2009-2018. See table below.

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

Powassan virus neuroinvasive disease cases reported by year, 2008–2017
Year Number of Reported Cases
2009 6
2010 8
2011 12
2012 7
2013 12
2014 7
2015 6
2016 21
2017 33
2018 21

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Data Table: In the United States, the number of Powassan virus neuroinvasive disease cases reported each year varies. From 2009 through 2018, an average of 13 cases were reported annually (range 6–33).

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Powassan virus neuroinvasive disease cases reported by state of residence, 2009–2018

Map of the United States showing Powassan virus neuroinvasive disease cases reported by state of residence, 2009–2018. See table below.

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

Powassan virus neuroinvasive disease cases reported by state of residence, 2008–2017
State Number of Reported Cases
Connecticut 3
Indiana 1
Maine 6
Massachusetts 22
Minnesota 34
New Hampshire 3
New Jersey 8
New York 19
North Carolina 1
North Dakota 1
Pennsylvania 6
Rhode Island 3
Virginia 1
Wisconsin 25

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Data table: From 2009 through 2018, Powassan virus neuroinvasive disease cases have been reported in Connecticut (3), Indiana (1), Maine (6), Massachusetts (22), Minnesota (34), New Hampshire (3), New Jersey (8), New York (19), North Carolina (1), North Dakota (1), Pennsylvania (6), Rhode Island (3), Virginia (1) and Wisconsin (25).

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Powassan virus neuroinvasive disease average annual incidence by county of residence, 2009–2018

 

Map of the continental United States showing the distribution of Powassan 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 0.20, 0.20 to 0.49, and greater than 0.50 per 100,000 population. Shaded counties are primary in Minnesota, Wisconsin, and New England states.

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

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This map shows the distribution of Powassan virus neuroinvasive disease average annual incidence by county of residence from 2009 through 2018. 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 primary in Minnesota, Wisconsin, and New England states.
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Additional Maps, Charts, and Tables

Powassan virus disease cases and deaths reported to CDC by year and clinical presentation, 2009-2018

Powassan 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. (%)
2009  6 0  (0)  0  0  (0)  6 0  (0)
2010  8 0  (0)  0 0  (0)  8 0  (0)
2011 12 1  (8) 4 0  (0) 16 1  (6)
2012 7 0  (0) 0 0  (0) 7 0  (0)
2013 12 2  (17) 3 0  (0) 15 2  (13)
2014 7 0  (0) 1 0  (0) 8 0  (0)
2015 6 1  (17) 1 0  (0) 7 1  (14)
2016 21 3  (14) 1 0  (0) 22 3  (14)
2017 33 2  (6) 1 0  (0) 34 2  (6)
2018 21 3  (14) 0 0  (0) 21 3  (14)
Total  133 12 (9)   11 0  (0)  144 12 (8) 

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

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Powassan virus disease cases reported to CDC by state of residence, 2009–2018

Powassan virus disease cases reported to CDC by state of residence, 2008–2017
State 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Total
Alabama 0 0 0 0 0 0 0 0 0 0 0
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 1 0 2 3
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 0 0 0 0 0 0 0 0 0 0
Georgia 0 0 0 0 0 0 0 0 0 0 0
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 0 0 0 0 0 0
Maine 0 0 0 0 1 0 1 1 3 0 6
Maryland 0 0 0 0 0 0 0 0 0 0 0
Massachusetts 0 0 0 0 1 4 3 5 3 6 22
Michigan 0 0 0 0 0 0 0 0 0 0 0
Minnesota 2 3 11 4 1 0 0 5 7 3 36
Mississippi 0 0 0 0 0 0 0 0 0 0 0
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 1 0 0 1 1 0 3
New Jersey 0 0 0 0 1 1 1 0 4 1 8
New Mexico 0 0 0 0 0 0 0 0 0 0 0
New York 3 1 0 1 5 1 1 2 6 4 24
North Carolina 0 0 0 0 0 0 0 1 0 0 1
North Dakota 0 0 0 0 0 0 0 0 1 0 1
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 1 0 0 0 0 0 4 1 6
Puerto Rico 0 0 0 0 0 0 0 0 0 0 0
Rhode Island 0 0 0 0 0 0 0 1 2 0 3
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 0 0
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 0 0 0 0 0 0 0 0 0
Virginia 1 0 0 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 4 4 2 5 2 1 5 3 3 29
Wyoming 0 0 0 0 0 0 0 0 0 0 0
Total 6 8 16 7 15 8 7 22 34 21 144

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

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Page last reviewed: July 10, 2019
Content source: Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID),
Division of Vector-Borne Diseases (DVBD)