The state was plunged into a snap five-day lockdown in February after more than 20 cases were linked to a cluster at the hotel.
The outbreak was traced back to a family of three who quarantined at the Holiday Inn and were believed to have been infected overseas.
One family member used a nebuliser for asthma despite them being banned outside of medi-hotels.
The nebuliser's use had initially been attributed to the spread of coronavirus at the hotel, with the belief the device was pushing the virus into the corridor.
The secret report says the virus instead may have escaped into the corridor as an unmasked woman was swabbed by a contracted health worker for a lengthy period of time, according to The Australian.
The publication said the Covid-19 Quarantine Victoria Infection Prevention and Control report from March claimed the virus had been contained to the woman's room before it "pooled outside the door" of the family after air conditioning pushed it from her open door down the corridor.
One of the adult family members likely became infected when they were picking up a meal from the corridor or taking out the rubbish, the report said.
It also suggests the virus then travelled further down the corridor and infected a food and beverage worker, and another employee who looked after the family during their entry and exit to the hotel.
After the reviewing of CCTV and interviews with employees, the report determined the virus was leaked from room 317 where the woman was swabbed, about five rooms away from the family with the nebuliser.
Man with nebuliser 'made to feel like criminal'
The returned Victorian traveller who was at the centre of the February cluster said he was made to feel like a criminal after claims his nebuliser – which health authorities said was not declared to them – sparked the outbreak.
He told The Age however he declared the machine to hotel quarantine staff and added he had not returned a positive Covid-19 test when he used the nebuliser.
The man added he was never told he could not use the device.
"If I was told that I couldn't use it, I never would have used it," he said.
“The way it has all come out in the news and through the government has made it sound like I was using it illegally, or that I have snuck it in or something like that.
“You are left feeling like a criminal or that you’ve done the wrong thing. That has been the hardest thing in all this.”
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