About 2,000 passengers from a cruise ship that docked in Sydney have been advised to quarantine themselves for a week in their homes or hotels after at least four cases of swine flu were confirmed on board, officials said Tuesday.
The passengers disembarked on Monday after nine days cruising Australia's Great Barrier Reef.
About 170 passengers reported as they disembarked the Pacific Dawn that they had flu-like symptoms or had been in contact with someone who had, state health officer Kerry Chant said.
By Tuesday, three passengers and a crew member had tested positive for swine flu with more diagnoses expected, Chant said.
Health authorities were contacting and monitoring passengers who were unaware of the onboard illnesses and urging them to stay indoors for seven days, Health Minister Nicola Roxon said.
The ship set sail Monday on another cruise to the Great Barrier Reef using some of the same crew.
Ann Sherry, chief executive of the ship's operator Carnival Australia, said the crew were taking the antiviral Tamiflu as a precaution.
"All the crew have been given Tamiflu so ... that's a very comprehensive set of requirements and actions that we've taken," Sherry told Australian Broadcasting Corp. radio.
Chant rejected criticism from some passengers that the crew should not have been allowed to leave.
"I think that the public health measures we put in place were appropriate to the circumstances that we were confronted with," she said.
Prof. Robert Booy, head of the National Center for Immunization, Research and Surveillance, said health authorities were right to let the ship sail.
"They've dealt with a lot of cruise ship outbreaks in the last few years for different infections so to the best of my knowledge, they are doing absolutely the right thing," he told ABC.
Australia has 44 confirmed cases of swine flu in the past two weeks, none of which were fatal.