Flickr / Ginny(Reuters) - One positive case of norovirus related to an investigation at restaurant chain operator Buffalo Wild Wings has been confirmed, the Kansas health department's Johnson County office said on Friday. Buffalo Wild Wings' shares fell as much as 13 percent to a 15-month low on Friday, before easing back to close down 8 percent at $142.08. The investigation is related to a gastrointestinal illness that affected at least 10 people who ate at a Buffalo Wild Wings' restaurant in Overland Park in suburban Kansas City. "These types of illness are common this time of year," Johnson County Department of Health and Environment Director Lougene Marsh said in a statement.