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Epidemiologists and public health experts have said it remains “critical” for New South Wales health authorities to track down the first case that led to transmission of Covid on Sydney’s northern beaches and, they argue, masks should now be mandatory.
The initial case that triggered the Avalon cluster – which has grown to more than 100 – has eluded authorities despite record rates of testing and strong contact tracing that has seen dozens of venues added to the alert list since the weekend. The northern beaches have been locked down until Wednesday night.
A professor of epidemiology at the University of Sydney, Alexandra Martiniuk, said it was “critical to determine how, where and when this first person of the newest outbreak became infected”.
“This is because once we know, we can all tighten procedures to make sure this doesn’t happen again. Tracking down this primary case should not be to blame them but instead to learn.”
The NSW chief health officer, Dr Kerry Chant, has said authorities have determined the virus was a US strain. But it is unclear how it spread possibly from a woman who arrived in Sydney on 1 December – and remains in quarantine – to the northern beaches community. Chant said identifying the first case of the cluster may be “a challenge beyond us”.
Contact tracing, genetic analysis and sewage analysis are all being used in NSW to identify the virus including the primary case on the peninsula. In the meantime, Martiniuk said, testing rates needed to be high to ensure the virus was contained. A record 60,000 people were tested in the 24 hours to 8pm on Wednesday.
“NSW Health is opening more testing centres, and several are open 24 hours, however there could be more because people are waiting up to six hours in some lines and some are being turned away when the centre closes for the night,” she said.
“Everyone should be wearing masks indoors in Sydney. But, of course, compliance is an issue. I live on the northern beaches and eye-balling it, it looks like only about 25% are wearing masks and some inappropriately, under their chin or not covering their nose. We could have some better public education about effective mask-wearing.”
The unknown person that brought the virus to the northern beaches has been referred to by some as “patient zero”. However, the term “patient zero” is reserved for the first human ever to be infected with Sars-CoV-2, the coronavirus that causes Covid-19). The term for the person who brought the virus to the northern beaches is the “primary case” in that cluster.
World Health Organization adviser and professor of epidemiology at the University of New South Wales, Mary-Louise McLaws, believes it is now unlikely the primary case will be found.
“But really it needs to be solved,” McLaws said. “We need to learn how it escaped quarantine so that we can tighten the system. I don’t understand why they can’t find the source case, unless that person has left the country and gone back overseas if, for example, they were a member of a flight crew.”
She said it could also be that the source case was asymptomatic. But she was concerned that person might have been in contact with people who travelled interstate for the holidays a couple of weeks ago, before border restrictions.
“It’s important to know who the source case is to work out, could this person have infected others even earlier than 7-8 December. The fact that the cluster happened in the northern beaches means that this person was likely in the area during the most infectious time. It’s somewhat good news that they may have been limited to that area during that infectious period, but until we find them we can’t be entirely sure.”
McLaws said the state’s excellent contact tracers had largely contributed to cases being contained to the northern beaches but luck had also played a part. If the primary case was asymptomatic, they would have been up to 40% less infectious than a symptomatic case, helping to limit the spread, she said.
“The government should order everybody across greater Sydney to wear a mask when they’re in public and not to travel outside of their postcode. I think because the government doesn’t want to be seen as having to resort to as harsh measures as Victoria, especially at Christmas, it’s stopping them from going harder. It’s stopping them from doing what they should.”
The co-director of the centre for virus research at The Westmead Institute for Medical Research, Prof Sarah Palmer, said contract tracing “has been phenomenal”. But knowing the primary case was important “to determine any breach in quarantine and to be confident in where they have been”.
“Until that person is identified, we don’t really know the entirety of the situation, and probably will never know. What this proves is that we have to remain diligent, and that complacency can lead to new infection in the community. If we don’t identify the primary patient, then what this new infection cluster is telling us is social distancing and public health measures must be maintained.”
However, Deakin University’s chair in epidemiology, Prof Catherine Bennett, said she was hopeful that even if the source case was not identified, the outbreak could be controlled.
“The longer that we do only find cases that are linked to the two initial hotspots, or contacts of those attendees, the more confident we can be there is not wider spread stemming from unknown transmission chains that started around the same time or earlier.”
But she too wants to see masks made mandatory across Sydney.
“At least when indoors and in share vehicles or public transport, and anywhere where you can’t keep your 1.5 metres space from people not from your household,” Bennett said.
Source: The Guardian
Keyword: Search for Sydney’s primary case ‘critical’, say epidemiologists who want masks made mandatory | New South Wales