Several cruise ships are being affected by a gastrointestinal illness called Norovirus lately. Celebrity and Fred Olsen cruise passengers have come down with the illness.

More than 300 passengers on the Celebrity Summit have come down with norovirus. Of the 2,113 passengers, 311 were sick and 14 of the 954 crew members had fallen ill.  "During its current sailing, Celebrity Summit has experienced an elevated number of persons with a gastrointestinal illness," Celebrity spokeswoman Cynthia Martinez confirmed with Cruise Critic. "Those affected by the short-lived illness have responded well to over-the-counter medication being administered onboard the ship."

As a way to fight the outbreak, Celebrity has enforced strict cleaning and disinfection procedures and has increased public announcements to let passengers know of the outbreak. A CDC officer will met the ship in Bayonne, New Jersey to conduct an investigation and make sure proper sanitation procedures are being conducted.

In response to the outbreak, which is affecting some 14.5 percent of passengers, Celebrity has amped up cleaning and disinfection procedures onboard Summit and increased public announcements to advise passengers of the outbreak.

Passengers who are infected will be compensated for the time they are confined to their cabins and those who are too uncomfortable to sail on the next trip can reschedule their sailings.

In addition to the Celebrity Summit, the smaller Fred Olsen ship, Boudicca is also being impacted, Cruise Critic reports. Out of the 763 passengers on the 10-night Baltic cruise, 85 passengers have fallen ill. This is the fifth outbreak on the ship this year. There was another outbreak just 10 days before on Fred Olsen's Black Watch.

Fred Olsen is also taking steps to clean the ship. It is not clear if passengers will be compensated. Boudicca will return to port in Belfast, where its current sailing originated, on Thursday, October 3. It will then undergo an extensive cleaning.

Those who come down with norovirus have symptoms such as vomiting, stomach cramps and fevers. It is not just limited to cruise ships thought. The virus can spread quickly when many people are together in a small space. This is why it also occurs in nursing homes, hotels and schools. The symptoms last roughly 24 to 48 hours.