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Human Powassan virus infections have been recognized in the United States, Canada, and Russia. In the United States, cases of Powassan virus disease (Powassan) 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.

Powassan cases are rare but the reported number of cases have increased in recent years. All residents of and visitors to areas where Powassan 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 is a nationally notifiable condition.  To ensure standardization of reporting across the country, CDC recommends that the national surveillance case definition be consistently applied by all state health departments.