Subtle changes of air pressure are enough to spread the coronavirus between rooms, but this has been an under-explored issue in the COVID-19 pandemic.

This is becoming evident in quarantine hotels – with experts warning that unaddressed aerosol transmission is causing the virus to leak despite lock-down protocols.

Health authorities are “scrambling” to investigate the mystery of the coronavirus “jumping” from one quarantine hotel room to another, which came to light on Wednesday in Melbourne.

While this case has been identified as the more transmissible UK strain, the virus isn’t just slipping through every open door – the demands of basic physics can explain what happened.

The real mystery is why it’s taken so long for airborne transmission of SARS-CoV-2 to be acknowledged as a serious problem.

Identical infections, days apart

On Wednesday, it was revealed that two parties of returned travellers – a family of five and a woman in her 60s – had tested positive for the highly infectious UK variant of SARS-CoV-2, while staying at the Park Royal Hotel under quarantine.

Genome testing showed the infections were identical but the parties had been infected on different days.

The family, who arrived from Nigeria on January 20, tested positive on January 24.

The woman, who occupied the opposite room, reportedly twice tested negative before testing positive on January 28.

Police Minister Lisa Neville told reporters: “That means it’s as if they have been in the same room together.”

Ms Neville said: “The viral load in the room of the family of five … was so high that just even opening the door to pick up your food has seen the virus get into the corridor.

“That is the working assumption.”

Staff in Victoria’s rebooted hotel quarantine program are COVID tested daily.

She noted there had been “absolutely no kids running down corridors or movement between the rooms at all”.

The hotel’s ventilation system will be reviewed, although Ms Neville said an earlier report had found no air was being shared between rooms or into common spaces.

“It’s probably unlikely to have been the ventilation system in this case,” she said.

According to reports, the infected woman remembers opening her door at the same time as another room in the hallway, but she has not been able to pinpoint the exact date or time.

The Australian Open has meant the arrival of international players and officials – bringing with them the virus. Photo: Getty

Basic physics would have done the job

There’s no suggestion that anybody coughed or sneezed when the doors opened.

So how did the virus travel from one room to another?

Physics and logic suggest the family’s room, with five people, may have been set at a cooler temperature than the woman’s room.

Warm air is thinner and creates lower pressure. Cold air creates high pressure.

Even a slight difference in temperature meant that, when the doors were opened, air from the infected family’s room would have quickly travelled to where air pressure was lower.

Air pressure is constantly changing to attain equilibrium. With those changes, there are air currents.

And it’s not really news that the coronavirus can viably hang in the air for hours – and therefore can be moved about during these pressure changes.

Victoria’s Deputy Chief Health Officer, Melanie Van Twest, begged off describing the event as aerosol transmission of the virus, saying she wasn’t “willing to put a name to it at the moment.”

It’s time someone did

Two weeks ago, senior scientists, health and safety experts and doctors told the ABC that failure at a federal level to acknowledge COVID-19 is transmitted through the air has been putting the community at risk.

The scientists said the virus “could be leaking through our border controls because authorities have not put in place precautions that provide the greatest possible protection from airborne transmission.”

The report noted the federal government’s health advisors had considered updating their advice on the airborne nature of the virus.

On Wednesday, Victorian authorities said they believe the COVID infection in a quarantine worker that has forced more than 1000 people into isolation may be due to airborne transmission of the deadly virus.

Experts again warned that if authorities don’t take aerosol transmission seriously, more infections are bound to leak from quarantine.