No reported cases of Norwalk virus on board.

Tests performed on the first group of people to get sick found the Norwalk virus.

On its last four cruises, more than 500 passengers and crew members fell ill, also with the Norwalk virus.

Outbreaks of the Norwalk virus are not unique to cruise ships.

"Well, you may have just introduced Norwalk virus onto the ship," he said.

The known viruses in the genus are all considered to be the strains of a single species called Norwalk virus.

The Norwalk virus, found on cruise ships, is highly infectious.

The Norwalk virus is passed from person to person and spreads quickly in a confined environment.

It can cause a more severe and longer-lasting illness than Norwalk virus.

Following this, in December, the hotel shut for ten days due to an outbreak of the Norwalk virus.