Passengers have been struck by an outbreak of gastric illness (GI) and confined to their staterooms for the second time this month on the 1,350-passenger mv Balmoral operated by Fred Olsen Cruise Lines.

It is not yet known how many travelers have been hit by the bug. Fred Olsen Cruise Lines confirmed the staff were attempting to contain the "extremely contagious gastric illness", just days after the cruise ship had underwent a "deep clean"’ in response to the earlier outbreak.

MV Balmoral is at the end of a 13-night round-trip voyage from Southampton to Madeira and the Azores. The ship is scheduled to return in Southampton today (May 24, Sunday), after leaving the city on May 11. The same day, Balmoral is expected to depart on a 7-night sailing to Amsterdam and Antwerp.

According to a spokeswoman for Fred Olsen, the number of guests affected was smaller than on the previous cruise. Passengers who were ill were required to remain in their staterooms, with complimentary room service, to minimise contact with others.

Hundreds of cruisers were hit by a vomiting bug (believed to be norovirus) earlier this month and the line had to cut short an 8-day sailing to the Norwegian fjords. The ship was carrying 1,163 passengers at the time. Due to the outbreak, Balmoral had to return to its home port a day early in order to be "systematically sanitised".

Some of the passengers who fell ill with stomach cramps, fever and diarrhoea, have contacted a law firm to investigate the cause of the illness.