Increasing the airflow through isolation hotels is important in helping prevent further spread of Covid-19, microbiologist Siouxsie Wiles says, though it's still not clear how the latest transmission happened.
Microbiologist Dr Siouxsie Wiles. Photo: RNZ / Dan Cook
Two people from north Auckland tested positive more than a week after they completed managed isolation at the Pullman Hotel, and a Northland woman who went through isolation at the same facility later tested positive.
Everyone who was at the Pullman Hotel in January will be tested, no new returnees would be sent there, and its staff would now not be allowed to move between facilities.
Air-conditioning in corridors in the Pullman Hotel isolation facility will be left on constantly to flush out air in common spaces.
"Increasing that air flow in the corridors to flush [virus particles] out is one really, really important thing " - Dr Siouxsie Wiles
Dr Wiles told Morning Report it is important to remember that almost all of the hundreds of people who had gone through the facility recently had tested negative.
She said increasing ventilation in the Pullman Hotel was a good move though it's also possible the virus could have spread through human error.
"The Northland case had a room that was opposite somebody else's room," Wiles said.
"If there are virus particles in the air of that room when you open the door they will end up going into the corridor.
"This is why increasing that air flow in the corridors to flush that out is one really, really important thing."
The two Auckland new cases were on a different floor of the Pullman Hotel to the Northland woman.
Wiles said more information was needed about the layout of the hotel, as well as checks on any other potential routes of transmission.
She said studies on ventilation in apartment blocks show that if the layout is the same from floor-to-floor there is potential transmission through pipes.
"If we know where the rooms are, that might help also understand whether there's been transmission that way."
"What we don't know is whether [transmission] is human error - whether people have had contact who shouldn't have had contact.
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The two former returnees were initially classified as under investigation after returning positive tests. The Ministry of Health said the pair returned a second positive test with a higher CT value which led to them being treated as confirmed cases.
A high CT value means the test is taking a while to become positive, Wiles said.
"That can happen because there's a low amount of viral material there, and it can happen when somebody is a historical case so they've got viral material but it's basically debris, it's broken up bits of virus that the immune system is still dealing with or it can be in the very, very early days of an infection, or the late stages.
"The fact that the value has gone up rather than gone down is news that would suggest they are not at the beginning of their infection.
"But it may mean it's historical or it's at the end of their infection when they're not likely to be infectious."
If it was a recent infection, she said, the CT value helped pin down when they might have been infectious, she said.
"My plea is if anybody has recently left the Pullman who hasn't heard from [health authorities] or returned their calls, please do, because it is so important that you do get tested.
"Of the hundreds of people who have been contacted almost all of them have tested negative.
"The numbers are on our side.
"I don't want everyone to be panicking or anything, but when you have any symptoms that are Covid-19 just remember that that's why we're asking people to get tested - to show whether there's been any transmission."
Wiles said it was good news that the two new cases appeared to be linked to MIQ, in terms of how to minimise transmission, and in ensuring there was no more virus or transmission in the community already.