NSW contact tracing teams ‘have lost the battle with Delta’ variant of Covid-19

The Delta variant has already defeated NSW contact tracers, public health experts say, with more cases every day than they can investigate.

The Service NSW app was designed to help contact tracers.

The Delta variant has already defeated NSW contact tracers, public health experts say, with more cases every day than they can investigate.

Some infectious disease specialists believe contact tracing was unable to keep up once 100 to 200 cases were recorded each a day. NSW recorded 818 cases on Monday, with just 47 known to have been isolated for the entirety of their infectious period.

University of Melbourne epidemiologist Tony Blakely said his modelling was based on the assumption that at just five cases contact tracers were able to reach 90 per cent of close contacts within three days.

“We assume that 90 per cent starts to fall as the case numbers go up in our models, that the maximum number of contacts per day is over 200, or 100 in some scenarios,” he said.

Professor Blakely said the Delta variant was moving too quickly for the 1000 contact tracers in NSW.

“Delta is such a pig, it takes away the window we used to have with the Wuhan variant of the virus,” he said. “The person who was infected didn’t start being infectious until day three or four of their infection, but with Delta they can start infecting people 24 hours after they’re infected. It’s reduced that window where they can find someone, throw them into quarantine and they become infectious in quarantine.”

ANU infectious diseases expert Peter Collignon said it was fair to say NSW had moved beyond being able to uncover significant details about each case.

“Once you’ve got more than 100 cases a day it starts getting stretched,” he said.

University of South Australia epidemiologist Adrian Esterman said the days of “gold standard” contact tracing, where investigators reached out to both close contacts and their close contacts after an infection was detected, were long gone.

“The gold standard of contact tracing is to do this double ring where you look at the close contact of the infected person which makes it, say, 10 and their close contacts to get to 100,” he said. “How many contact tracers are you going to need when you have a thousand cases?”