All cruise ships arriving with flu on board will now be treated as if they have swine flu, with decisions then made on a case by case basis, chief health officer Kerry Chant said.

The response will mean people will not be let off the ship until the vessel has been cleared of swine flu, as well as asking passengers to isolate themselves until tests are done.

Health authorities have come under fire after allowing passengers to leave the P&O ship Pacific Dawn.

Although the ship had not been in any area where the virus is present, 18 people have since tested positive to it.

As of today, 598 NSW residents have been assessed by public health experts for human swine influenza, with 265 suspected cases and 315 released after assessment and testing.

``At the moment the situation in NSW is we have cases we're picking up at airports and a large number of cases generated through the Pacific Dawn cruise we don't have demonstrated community transmission,'' Dr Chant said.

``Our investigations have to be detailed, we have to investigate a number of leads before I'm happy to conclude how the original cases acquired their infection.''

Dr Chant said at this time there would be no measures taken to stop large sporting events or crowds, but if there needed to be, health officials would approach the government to implement them.

All NSW ministers have also been caught up in the scare, as Tourism Minister Jodi McKay attended a cabinet meeting after travelling on a plane returning from the United States with six infected passengers.

Ms McKay, her chief of staff and the state's chief scientist decided to withdraw from public engagements as a precaution.

Health Minister John Della Bosca said health advice given said there was no need for ministers to isolate themselves, and Ms McKay had made her own decision.

Anyone who has returned from the Mexico, USA, Canada, Japan or Panama in the past week should look out for symptoms including fever, rhinorrhoea, nasal congestion, sore throat or cough.

Symptoms will generally appear between two to four days after exposure.

Anyone who has recently returned from the affected areas and who develop any symptoms of breathing difficulties should contact their local public health unit, general practitioner or emergency department.

Details: www.health.nsw.gov.au/publichealth/swine_flu.asp