The Centers for Disease Control and Prevention is investigating a Seoul virus outbreak in pet rats and people exposed to rats at breeding facilities in Wisconsin and Illinois, the agency said in a health advisory this week. Eight people were infected in Wisconsin and Illinois, two of which were hospitalized, and residents in at least 10 other states also may have infected rats, CDC said. People infected with the hantavirus often exhibit mild or no symptoms, but some may develop a form of hemorrhagic fever with renal syndrome. CDC recommends testing people who report current or recent illness after handling rats from a facility infected with the virus or which sold rats to an infected facility. Health care providers should report any suspected cases of the virus to their state or local health department, which also can answer testing inquiries, the agency said.