May 29 (Bloomberg) -- Carnival Corp.’s luxury cruise ship Pacific Dawn was asked not to stop at ports in north Queensland after dozens of people caught swine flu while sailing in the South Pacific, Australian health officials said.

Fifty-three passengers and crew have tested positive for the H1N1 virus after two voyages on the 11-deck vessel. Most patients had a “mild illness” and were diagnosed after they disembarked in Sydney May 25, the New South Wales government said. Pacific Dawn, with three infected crew members, was rerouted to reach Brisbane, Queensland’s capital, tomorrow, the state’s health department said.

“All passengers will be screened before disembarking and any passengers with symptoms will be swabbed and provided with masks and a course of Tamiflu,” Jeanette Young, Queensland’s chief health officer, said in a statement, referring to Roche Holding AG’s anti-flu medicine.

Cases among people on board the ship have been found in Canberra and the states of New South Wales, Queensland, South Australia and Victoria, the nation’s health department said by e-mail today. The infections contributed to a more than twofold increase in Australia’s swine flu tally to 164 since early yesterday.

Victoria’s health department said 3 more cases were confirmed overnight, bringing its total to 99. About 82 percent were from the northern area of suburban Melbourne. Five schools have been shut to reduce transmission. Of 46 people diagnosed with swine flu since midday yesterday, 29 were school children, Daniel Andrews, the state’s health minister, said in a statement.

Tourist Spots

Miami-based Carnival’s Australian unit was asked to alter the itinerary of the Renzo Piano-designed Pacific Dawn to avoiding docking at Cairns and Port Douglas and minimize the risk of the virus spreading through Queensland’s major tourist centers, the state’s health department said.

The 795-cabin cruise ship, which boasts a casino, jogging track and five restaurants, is scheduled to arrive June 1 in Sydney with more than 1,800 passengers.

The pig-derived virus is the main flu strain currently circulating in Australia, which is approaching the winter influenza season, said Ian Barr, deputy director of the World Health Organization Collaborating Center for Influenza in Melbourne. The center is one of four laboratories globally that provides the WHO with data on flu cases and advises which strains to include in vaccines.

“They are picking it up in isolated cases in the community,” Barr said by phone yesterday. “Whether it’s truly community-wide is probably a bit too early to say.”

Pandemic Potential

Most of those infected in Australia have been linked to international travel or relatives of other confirmed cases, Barr said. The WHO said swine flu would touch off the first influenza pandemic in 41 years if it causes epidemics outside North America similar to the ones identified in Mexico and the U.S. about six weeks ago.

Forty-eight countries have officially reported 13,398 cases, including 95 deaths, the Geneva-based WHO said May 27. The tally excludes 1,163 additional cases in the U.S., 433 in Mexico, 197 in Canada, 128 in Australia, 79 in Chile, 66 in the U.K., 18 in Argentina, 26 in Spain, 12 in South Korea, 8 in the Philippines, 5 in Brazil, 3 each in Singapore and Italy, 2 in Switzerland, as well as initial infections in Bolivia, Romania, Slovakia, Uruguay and Venezuela that were announced subsequently.

Rapid Spread

Global cases have more than doubled in the past two weeks as the virus became established in Western Europe, Japan, South America and Australia. Japan, with the most infections after Canada, Mexico and the U.S., said 360 people have caught the bug, mostly students in the prefectures of Osaka and Hyogo.

“There isn’t much difference between a high school in Osaka and a luxury cruise liner in the South Pacific -- they are both ideal breeding grounds for this virus,” said Peter Cordingley, a Manila-based spokesman for the WHO’s Western Pacific region.

The infections on the Pacific Dawn may have stemmed from a 5-year-old boy who developed symptoms two days after starting the voyage to New Caledonia, Loyalty Islands and Vanuatu, said Anthony Fisk, a spokesman for Carnival Australia. The boy was diagnosed with the new strain, which was subsequently found in three people who had direct contact with him, Fisk said.

More Cases Suspected

Queensland authorities confirmed its 10th swine flu case, in a Pacific Dawn passenger who got off the ship in Sydney. Eight of the state’s total were travelers on the vessel and don’t include the three infected crew still on board. Test results on 11 suspected cases are pending, Queensland Health said in a statement today.

South Australia’s health department said yesterday three people in contact with a confirmed case from Pacific Dawn have the bug. “It is likely that more passengers from the Pacific Dawn will come forward for testing and management,” Ann Koehler, director of the department’s communicable disease control branch, said in a statement today.

Of the 48 confirmed cases in New South Wales, 38 have been associated with the Pacific Dawn cruise, the state’s health department said in a statement today.

Under new protocol for arriving cruise ships, the New South Wales government will treat flu-like symptoms on such vessels as swine flu, pending tests to clear any infected people, state Health Minister John Della Bosca said in a May 27 statement.

Carnival said in a statement it is introducing measures to reduce risks, including screening passengers for flu before boarding and asking people with flu-like symptoms to report immediately to the ship’s medical center, where passengers will receive free treatment.

The company said May 18 that changing cruise itineraries because of a U.S. government recommendation against non- essential travel to Mexico, due to swine flu, may hurt earnings by 5 cents a share, the majority of which will be taken in the fiscal second quarter.

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net.

Last Updated: May 29, 2009 02:27 EDT