Victoria's contact tracing system waned as daily COVID-19 cases hit about 200 cases, Chief Health Officer Brett Sutton admits, although improvements have pushed that figure out.
Reflecting on the state's deadly second wave, Professor Sutton told an inquiry into its oft-panned contact tracing regime that authorities couldn't keep up when new cases reached low triple figures.
"It's probably at that kind of level when you get to 200 or more cases per day, it starts to really challenge your ability to get to all of that timely information for the close contacts... within that critical time period," he said.
Professor Sutton is "confident" cases won't rise to that point again, with the state notching its 24th day without a new infection or death.
His comments follow Australia's chief scientist Dr Alan Finkel suggesting before the inquiry last week that tracing efforts were easily overwhelmed at the height of Victoria's crisis.
Newly-appointed Department of Health and Human Services secretary Euan Wallace said close contacts averaged 10 per case, as daily infection peaked over 700 in early August.
That meant identifying 7000 close contacts each day, a feat he said no Australian jurisdiction could manage.
"The processes that were in place and every other state and territory around the country just could not cope with those new numbers every day," Professor Wallace told the inquiry.
Victoria has since moved to a digitised system, created by US tech firm Salesforce, which automates the process "end to end".
Prof Wallace said it and other improvements had put Victoria in a position where it "could cope with 500 new cases a day".
The Salesforce-built system will be fully integrated by December, but it was revealed last week the company offered its services to the state government in March.
None of the senior DHHS officials appearing before the inquiry, headed by Reason Party MP Fiona Patten, were aware why the offer was initially knocked back.
"It's not a case of a refusal per se," Prof Wallace said.
"There was a number of approaches made to the department."
Professor Wallace said the department's previous IT platform didn't sort negative and positive test results, slowing down the identification of confirmed cases and initiation of contact tracing.
"Essentially the positive results were being held up by the negative results," he said.
"So a very important decision was made to triage, or filter off the negative results to allow positive results to come in immediately.
"That probably saved us 24 hours in the 'every minute counts' approach."
DHHS testing commander Jeroen Weimar said a quarter of those being tested for coronavirus across the state were not symptomatic.
He said nasal swabs had been made "far less probing" in the past few months, and salvia-based testing deployed for the asymptomatic surveillance program.
The Legislative Council Legal and Social Issues Committee is investigating whether the contact tracing system as it stands can handle future coronavirus outbreaks.
Australian Associated Press