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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, 2008–2017

Graph showing Powassan virus neuroinvasive disease cases reported by year, 2007-2016. 7 cases reported in 2007, 2 in 2008, 6 in 2009, 8 in 2010, 12 in 2011, 7 in 2012, 12 in 2013, 7 in 2014, 6 in 2015, and 21 in 2016.

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
2008 2
2009 6
2010 8
2011 12
2012 7
2013 12
2014 7
2015 6
2016 21
2017 33

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Data Table: In the United States, the number of Powassan virus neuroinvasive disease cases reported each year varies. From 2008 through 2017, an average of 11 cases were reported annually (range 2–33).

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

Map of the United States showing From 2008 through 2017, POWV neuroinvasive disease cases have been reported in Connecticut (1), Maine (3), Massachusetts (13), Minnesota (25), New Hampshire (2), New Jersey (3), New York (17), North Carolina (1), Pennsylvania (1), Rhode Island (1), Virginia (1) and Wisconsin (20).

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 1
Maine 6
Massachusetts 16
Minnesota 32
New Hampshire 3
New Jersey 7
New York 16
North Carolina 1
North Dakota 1
Pennsylvania 5
Rhode Island 3
Virginia 1
Wisconsin 22

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Data table: From 2008 through 2017, Powassan virus neuroinvasive disease cases have been reported in Connecticut (1), Maine (6), Massachusetts (16), Minnesota (32), New Hampshire (3), New Jersey (7), New York (16), North Carolina (1), North Dakota (1), Pennsylvania (5), Rhode Island (3), Virginia (1), and Wisconsin (22).

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

 

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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Data Table: This map shows 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.
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Additional Maps, Charts, and Tables

Powassan virus disease cases and deaths reported to CDC by year and clinical presentation, 2008-2017

Powassan 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 2 0  (0) 0 0  (0) 2 0  (0)
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)
Total  114 9 (8)   11 0  (0)  125 9 (7) 

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, 2008–2017

Powassan virus disease cases reported to CDC by state of residence, 2008–2017
State 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 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 0 1 0 1
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 0 0
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 0 1 0 1 1 3 6
Maryland 0 0 0 0 0 0 0 0 0 0 0
Massachusetts 0 0 0 0 0 1 4 3 5 3 16
Michigan 0 0 0 0 0 0 0 0 0 0 0
Minnesota 1 2 3 11 4 1 0 0 5 7 34
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 0 1 0 0 1 1 3
New Jersey 0 0 0 0 0 1 1 1 0 4 7
New Mexico 0 0 0 0 0 0 0 0 0 0 0
New York 1 3 1 0 1 5 1 1 2 6 21
North Carolina 0 0 0 0 0 0 0 0 1 0 1
North Dakota 0 0 0 0 0 0 0 0 0 1 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 0 1 0 0 0 0 0 4 5
Puerto Rico 0 0 0 0 0 0 0 0 0 0 0
Rhode Island 0 0 0 0 0 0 0 0 1 2 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 0 1 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 0 4 4 2 5 2 1 5 3 26
Wyoming 0 0 0 0 0 0 0 0 0 0 0
Total 2 6 8 16 7 15 8 7 22 34 125

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

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Page last reviewed: December 4, 2018
Content source: Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID),
Division of Vector-Borne Diseases (DVBD)