Wisconsin, USA (initial cluster)

Multi-state Seoul virus (SEOV) outbreak linked to home-based pet rat (Rattus norvegicus) breeding facilities ('ratteries') first identified in Wisconsin in December 2016. The trace-forward investigation ultimately identified 31 facilities with human and/or rat SEOV infections in 11 U.S. states (Colorado, Georgia, Iowa, Illinois, Minnesota, Missouri, Pennsylvania, South Carolina, Tennessee, Utah, and Wisconsin), with rat exchanges to Canadian ratteries. Of 183 persons tested, 24 had SEOV antibodies (17 U.S. and 1 Canadian resident with recent infection, plus 4 U.S. and 2 Canadian residents with past infection). Eight U.S. patients were symptomatic, three were hospitalized with mild HFRS, and no deaths were reported.