Victoria’s rise in Covid-19 case numbers is occurring so rapidly that contact tracing can no longer be relied upon to unearth all potential clusters in the state, according to epidemiologists who argue health detective work “won’t make much difference when you’ve got thousands of active cases potentially out there”.
On Tuesday morning, Brendan Murphy, secretary of the Department of Health, told the senate select committee on Covid-19 that delays had plagued Victoria’s contact tracing regime “certainly for a period of a couple of weeks”, and that the backlog “has to have been a factor” in community transmission. However he said the state had made substantial improvements to contact tracing recently.
His comments came after Victoria’s chief health officer, Brett Sutton, on Monday said there were “literally thousands on the phone who are chasing up close contacts and who are talking to them about what quarantine requires of them”, after reports that some close contacts of confirmed cases were waiting up to a week for contact from the state instructing them to self-isolate.
Contact tracing involves interviewing confirmed cases, calling their close contacts to let them know isolation requirements, as well as checking up on those in isolation and investigating links between individual cases and possible clusters.
In late July, Sutton warned that each new Covid-19 case required an average of seven to nine phone calls, each up to an hour in length, to trace close contacts, meaning the 3,556 cases under investigation in Victoria on Monday could require more than 32,000 phone calls.
The Guardian understands there are about 2,000 people supporting Victoria’s contact tracing scheme as of this week, and at least 1,000 of these Department of Health and Human Services staff members are undertaking non-clinical tracing work, primarily phone calls, as opposed to investigating links and potential clusters.
By contrast, in the seven days leading up to last Friday, NSW Health’s more than 300 contact tracing staff made calls to 4,985 close contacts of the 94 community transmitted cases in the state – more than 50 calls for each case – to inform them of their self-isolation requirement.
The DHHS declined to specify the number of clinical contact tracers working in Victoria each day, but it has increased significantly since before the pandemic. A leaked document suggested the DHHS had just 14 contact tracers in March.
The federal government has so far provided 30 staff to the effort since the resurgence of the virus in the state, with further help from the defence force to door-knock, as well as call staff from states including New South Wales, Western Australia, South Australia and Queensland.
Peter Collignon, a professor of infectious diseases at the Australian National University, told the Guardian the situation in Victoria had deteriorated so much that contact tracers in the state could not work as extensively on each case as their counterparts in NSW.
Collignon said that after reports that one in four confirmed Covid-19 cases were not at their homes when tracers knocked on their front doors last week, authorities had to focus on preventing people engaging in behaviour that spread the virus, as opposed to following up with all close contacts of cases days after a diagnosis.
“The sheer numbers coming out of Victoria each day make contact tracing difficult. What’s important now is stopping people with known infections moving in the community, making sure they’re staying at home.
“Victoria has got so much community transmission, that finding one of those early clusters [like in NSW] won’t make much difference when you’ve got thousands of active cases potentially out there,” Collignon said.
Gerard Fitzgerald, emeritus professor of public health at Queensland University of Technology, said that as cases in Victoria continued to grow there would be more “overlap” in close contacts of cases, somewhat alleviating the number of phone interviews necessary.
But he said this was unlikely to make enough difference when more than 500 cases were diagnosed each day.
“Any additional stress is going to make the contact tracing work more difficult because they’ve got to go back three or four days already … If the numbers can’t be kept down, then at some point there’s probably going to be no chance of tracing every case.
“There’s no doubt that the principal strategy for breaking the pandemic in Victoria now can’t be on contact tracing, it has to fundamentally be on stopping the behaviour of individuals, getting them into isolation,” Fitzgerald said.
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