( CNN ) -- The outbreak of a gastrointestinal illness has spread to more passengers on a U.S. cruise ship , with nearly 450 falling sick while at sea , the cruise company said Tuesday . The Celebrity Cruises ship Mercury departed Charleston , South Carolina , February 15 and headed for the eastern Caribbean , according to a Celebrity Cruises statement . On the way , 419 of the 1,838 passengers fell ill , along with 27 of the 849 crew members , the cruise line said . The number of affected passengers increased from the 353 reported the day before . Their symptoms included upset stomach , vomiting and diarrhea , Celebrity Cruises spokeswoman Cynthia Martinez said . Guests who were in isolation while ill will receive compensation , she said . The sickened passengers and crew have been administered over-the-counter medicine and are responding well , Celebrity Cruises said . But it is still unclear how they became sick , Martinez said . Medical samples will be sent to a lab for testing Tuesday , she added . The ship 's medical facility first started treating guests Sunday , Martinez said , and by Monday , hundreds of others were sick , too , Celebrity Cruises reported . A doctor and two nurses joined the cruise medical staff Monday to help with the overload of patients when the ship stopped in Tortola , British Virgin Islands , according to the statement . The ship does not return to Charleston until Friday and will be at sea until then , Martinez said . To control the outbreak , the crew has stepped up cleaning of the ship , which is advised by the Centers for Disease Control and Prevention when an outbreak of gastrointestinal illness occurs . Norovirus commonly causes viral gastrointestinal illness outbreaks on cruise ships , the CDC says . It can spread from contact with contaminated food or drink , by touching objects infected by people who are already sickened , or through close contact with people who are infected , according to the CDC . So far this year , three gastrointestinal illness outbreaks have occurred on cruise ships that docked at a U.S. port , according to the CDC . Norovirus was the cause of two outbreaks on the Mercury in 2009 , the CDC reported . The outbreaks reported and investigated by the CDC infected at least 3 percent of the people onboard the cruises carrying at least 100 passengers for anytime between three days to three weeks .
Celebrity Cruises ship departed South Carolina on February 15 and headed for the Caribbean . Passengers and crew aboard come down with gastrointestinal illness . They have been given over-the-counter medicine and are responding well , cruise line says .