Eight passengers on a riverboat cruise of the Ohio River remained hospitalized in western Kentucky on Saturday after developing flu-like symptoms while aboard the boat.

The Mississippi Queen passengers were part of a group taken to Methodist Hospital on Friday evening. More than 30 had reported that they were ill, including 22 who suffered from nausea and vomiting, hospital officials said.

Hospital spokeswoman Shelia Patterson said 17 passengers were treated. Nine were released late Friday, while eight others were kept overnight for observation.

None of the illnesses appeared to be life-threatening.

The cause of the outbreak was still under investigation. An epidemiologist was sent to the boat by the federal Centers for Disease Control and Prevention, said April Matson, a spokeswoman for Majestic America Line.

The riverboat left Cincinnati on Wednesday and was scheduled to arrive in St. Louis on Tuesday. The majority of the ship's 525 passengers remained on the ship Saturday as it continued its tour, Matson said.

The company is a subsidiary of Ambassadors International Inc., a cruise, marine, and travel and event company based in Newport Beach, Calif. Majestic America Line owns six cruise ships that ply U.S. coastal and inland waters, and rivers.

The boats travel the Mississippi, Ohio, Tennessee, Cumberland and Arkansas rivers in the Midwest and South, and the Columbia, Snake and Willamette rivers in the Northwest. The company also operates cruises of Alaska's Inside Passage.