Quarantine worker’s false-negative test stalled discovery of Coburg exposure site

Victoria’s public health team was stymied for several days in identifying a high-risk exposure site that a hotel quarantine worker with coronavirus visited, because she had initially returned an “exceptionally rare” false-negative result.

Authorities are confident they have ring-fenced a growing COVID-19 cluster linked to a private function at the Coburg site on February 6, after an additional two people who attended the event tested positive for coronavirus on Sunday.

The venue (centre) in Sydney Road, Coburg, that has been listed as a COVID-19 exposure site.Credit:Ashleigh McMillan

A three-year-old and a woman aged in her 50s were the latest people to contract the virus, bringing the size of the cluster that began at Melbourne Airport’s Holiday Inn hotel to 16. The Department of Health believes the Holiday Inn cluster is linked to a transmission event on February 3 or 4 when a returned traveller, who later tested positive to the UK variant of the virus, had used a nebuliser. 

The Coburg venue where three close contacts are now confirmed to have contracted COVID-19 was not listed as an exposure site until late on Friday – two days after the hotel quarantine worker tested positive. Chief Health Officer Brett Sutton said the venue had not been on the radar of the public health team as a potential site because the COVID-19 Quarantine Victoria staff member, who attended the February 6 event, had tested negative for the virus the following day.

“We now know with laboratory testing of the sample that it was a weak positive,” Professor Sutton said. “When you’ve got a negative test the day after an event, it’s not in scope as an exposure for someone who is potentially infectious because you don’t imagine them to be infectious.”

Nasal and throat swab testing has a sensitivity rate of 99 per cent, and Professor Sutton reassured Victorians a false-negative result was an infrequent occurrence.

“It is highly unusual to get a negative test on someone who was later found to be positive, and in fact, transmitted to other people,” he said.

“To be a weak positive but to pass on to others is unusual. But we have to be agile in our response and understand that that was a transmission event, and wrap the public health response around everyone who was here.”

Authorities identified the function venue at 426 Sydney Road, Coburg, as a high-exposure site late on Friday after a man aged in his 30s from Point Cook, who attended the venue with family members including the hotel quarantine worker on February 6, tested positive.

Everyone at the venue has been identified and contacted, but following the two new confirmed cases on Sunday two swim centres, a bakery and a supermarket in Melbourne’s north were added to a growing list of high-risk exposure sites.

Chief Health Officer Brett Sutton says it is “exceptionally rare” to record a false-negative result. Credit:Getty Images

A positive case attended Elite Swimming Pascoe Vale on February 8 between 5pm and 6pm and the Oak Park Sports and Aquatic Centre in Pascoe Vale between 4pm and 7.30pm on February 10.

A positive case also shopped at Woolworths at Broadmeadows Central on February 9 between 12.15pm and 12.30pm, followed by a nearby Ferguson Plarre bakery from 12.30pm to 12.45pm.

The four new exposure sites are listed as Tier One, which means anyone who visited them during the times outlined must immediately test and isolate for 14 days regardless of the initial test result.

Professor Sutton said it was reassuring there were a number of negative tests for those at the Coburg venue.

“They are all in quarantine now,” he said, and they would be retested multiple times before their quarantine period ended. “We’re going to be very highly focused on this event and this cohort of individuals who … have been fantastic in their co-operation with the department.”

COVID-19 response commander Jeroen Weimar addresses media on Sunday.Credit:Getty Images

COVID-19 response commander Jeroen Weimar said the state government believed the worker contracted the virus on February 3 or 4 and was infectious at the time of the Coburg event.

“People who are at the heart of all of this have been co-operating fully and have done what they needed to do,” he said. “That’s why we’ve been able to close down all the other lines of inquiry. That’s why we have in the region of 30 negative tests coming out of the event on Saturday, February 6, and all the other positives are now contained, as are the primary close contacts.”

Health Minister Martin Foley said the number of close contacts linked to the Holiday Inn cluster had reduced from 996 on Saturday to 940 on Sunday, of which 129 are direct family members.

He also announced the state had tripled its testing capacity at public laboratories, which can now process about 30,000 tests a day and return results in less than 24 hours.

As well as the two locally acquired cases, Victoria recorded one new case in hotel quarantine on Sunday.

Opposition health spokeswoman Georgie Crozier said Premier Daniel Andrews needed to “end his arrogance, his spin and ask for help”.

“I implore you, ask for that help,” she said. “Victorians are fed up with your spin and they just want their systems fixed.”

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