A NSW public health official thinks he would have assessed the Ruby Princess as being a medium COVID-19 risk ahead of the ill-fated cruise ship's arrival in Sydney, had he considered a guideline change during his assessment.
The ship was instead given a low risk rating, with passengers allowed to disembark and disperse before testing revealed there had been COVID-19 cases on board.
South Eastern Sydney Local Health District's Mark Ferson was one of several health experts involved in assessing the ship's coronavirus risk before it docked in Circular Quay in mid-March.
In written evidence to a special commission of inquiry, Professor Ferson thought he would have assessed the ship as a medium risk if he thought of a guideline change, which included all international travel in "suspect case" criteria.
The update to Communicable Diseases Network Australia guidelines was not reflected in the risk assessment form, Prof Ferson said.
He said he had considered the Ruby Princess low risk for number of reasons, including the number of positive Influenza A diagnoses and the fact that COVID-19 tests performed when the ship was in Wellington had come back negative.
NSW Health's communicable disease senior medical officer Sean Tobin also now believes the ship should have been classified as a medium risk, the inquiry previously heard.
Dr Tobin last week said health authorities had considered passengers' onward travel, including flights home, when allowing them to disembark.
Prof Ferson's written evidence said in a medium risk scenario, all passengers and crew who weren't swabbed for COVID-19 might be allowed to disembark after the ship was boarded for health screening.
But he told the inquiry on Monday that disembarkation wouldn't have necessarily happened in the Ruby Princess case, if the ship was assessed as medium risk.
The professor said they didn't want people to miss travel connections but he thought "in practice we would likely have kept the whole ship until we received the (COVID-19 test) results".
The inquiry continues.