On 24 January 2017, the United States Centers for Disease Control and Prevention (CDC), through their Health Alert Network (HAN) publication, reported 8 cases of infection with Seoul virus in the states of Wisconsin (n=2) and Illinois (n=6). The first two cases were reported in early December 2016, when two home-based pet rat breeders in Wisconsin State developed an acute febrile illness, later confirmed as Seoul virus infection. Rats (Rattus norvegicus) at some facilities also tested positive for Seoul virus. Human infection with Seoul virus is not commonly found in the United States; this virus family also includes Sin Nombre virus, which is the most common hantavirus causing disease in the United States. This is the first known outbreak associated with pet rats in the United States.