The cruise ship Celebrity Mercury continues to be plagued by illnesses.

Since the ship set sail from Charleston on Saturday, 55 of the 1,880 passengers have fallen ill with a stomach bug known as norovirus, cruise line spokeswoman Cynthia Martinez said late Wednesday in an e-mail. She could not be reached Thursday for an update.

The recent spate of illnesses follows a much larger outbreak on the ship's previous voyage late last month, during which more than 400 passengers and dozens of crew members fell ill with the bug.

The Mercury's most recent departure was delayed a day as a cleaning crew sanitized the ship, and three officials with the Centers for Disease Control and Prevention went aboard to test for the virus.

Officials with the State Ports Authority and the Charleston Area Convention and Visitors Bureau coordinated with Celebrity to help stranded passengers enjoy their unplanned layover in Charleston.

Norovirus symptoms include nausea, vomiting, diarrhea and stomach cramps, sometimes accompanied by a low-grade fever. The highly contagious illness usually lasts a day or two and spreads through food, water or person-to-person contact.

Norovirus generally affects confined communities such as cruise ships, schools and hospitals. The S.C. Department of Health and Environmental Control has investigated twice the usual number of gastrointestinal illness clusters across the state this year.