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.
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.
"The park is reminding all employees and visitors to wash their hands frequently and stay home if they experience any symptoms of a gastrointestinal illness,” Gediman said in a statement.
A message seeking comment from a spokesman for Aramark has not been returned.
Aramark received numerous complaints from visitors about poor food quality, shuttle service and other services since it began managing Yosemite's concessions four years ago.
The Ahwahnee Hotel lost its prestigious four-diamond rating by AAA, a distinction the luxury hotel held since 1991, and is now listed as a three-diamond hotel. Visitors to the hotel at the foot of the iconic Half Dome have included Queen Elizabeth II and U.S. presidents.