A viral bug is the likely cause of an outbreak of gastroenteritis on a luxury cruise liner, New South Wales health authorities say.

About 182 passengers fell ill on the Explorer of the Seas which has just docked in Sydney.

Public health director with the South East Sydney Local Health District, Dr Mark Ferson, said the outbreak started a couple of days after the ship left Sydney on December 2 and spread quickly.

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“It’s probably a highly infectious virus called norovirus which causes diarrhoea and vomiting,” he said.

The cruise line operator Royal Caribbean took proper steps to stem the contagion, Dr Ferson added.

“They’re very professional and they’ve instituted extra cleaning sanitation, getting passengers to wash their hands more, doing extra cleaning in the terminal of the ship in ports,” he said.

The cruise liner Explorer of the Seas has docked in Sydney.

“These outbreaks do occur from time to time and because the outbreak is so infectious it’s quite hard to control.”

The ship carries about 4,700 passengers and crew.

Dr Ferson said although the viral outbreak is classified as large, it is not unprecedented.

“Outbreaks of this magnitude, that we’re aware of, do occur on cruise ships coming into Sydney several times a year,” he said.

“The virus is very tricky it changes every few years, so it’s a bit like flue virus in that it changes from time to time.

“When that happens more people are susceptible to the illness and likely to be infected.”

In a statement, Royal Caribbean said “those affected by the short-lived illness have responded well to over-the-counter medication administered onboard the ship”.

“The ship and terminal will undergo enhanced cleaning and sanitisation to prevent any illness affecting future cruises,” the statement said.

“All new guests embarking will receive a letter at boarding that asks them to advise if they have experienced any gastrointestinal symptoms within the last three days.”