MIAMI (CBSMiami) – More than 300 passengers and crew have fallen ill on Royal Caribbean’s “Explorer of the Seas”.

The U.S. Centers for Disease Control said health officials will board the ship Sunday while it’s docked in St. Thomas in the U.S. Virgin Islands.

The CDC said 281 passengers and 22 crew members are ill.

It’s not clear at this time what is causing the widespread illness, but it could be the norwalk virus. The CDC said symptoms include vomiting and diarrhea.

Royal Caribbean said they are increasing disinfection procedures and readying new crew members to join the ship.

Earlier this month 68 people on the cruise line’s “Majesty of the Seas” came down with flu like symptoms.

When the it docked at Port Miami, the Royal Caribbean conducted an extensive cleaning onboard the ship and the cruise terminal.

According to health experts, each year as many as 300 million people worldwide are affected by Norovirus. Only the common cold is more prevalent.