A large number of Genesee County residents have been experiencing a flu-like virus that makes people severely ill with diarrhea and vomiting, and it seems to be spreading across the county.County health officials say the stomach-churning outbreak may continue to grow.County Healt Department chief MarkValacak told the county board of commissioners that norovirus outbreaks have already been reported by the Grand Blanc School District. The virus is highly contagious.