YOSEMITE NATIONAL PARK, Calif. (AP) — Federal health officials are inspecting Yosemite National Park’s food service areas after at least a dozen people have fallen ill with stomach issues.

The National Park Service and the U.S. Public Health Service told the San Francisco Chronicle they launched an investigation after employees and visitors reported the problems this month.

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Federal officials said they haven’t identified the illness or the origin of the outbreak. Park officials said those who had gotten sick are getting better or already recovered.

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Federal officials were working with Aramark, the concessionaire that operates Yosemite’s restaurants, snack shops and hotels, to clean up and disinfect food service facilities in the park, including the famous Ahwahnee Hotel, Yosemite spokesman Scott Gediman said.

“The park is reminding all employees and visitors to wash their hands frequently and stay home if they experience any symptoms of gastrointestinal illness,” Gediman said in a statement.

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A message seeking comment from a spokesman for Aramark has not been returned.