Early on Thursday afternoon, 10 days after a grocery trip in locked-down Sydney, Natalie Barker’s phone lit up with some wholly unsurprising news.
“This is a message from NSW Health,” the text read. “A person who attended Tramshed Sydney in Forest Lodge … has tested positive for Covid-19. All people there at the same time are advised to get tested for Covid-19 as soon as possible and self-isolate until you receive a negative test result.”
Barker had already worked out she was a contact of the case two days earlier, largely by luck. Her housemate had noticed the Tramshed on NSW’s list of exposure sites and, knowing that’s where Barker did her grocery shopping, gave her a heads up.
Barker isolated and got tested. All the while, she heard nothing from NSW Health, until Thursday’s belated text.
“I was just a bit shocked, because I thought it would come through straight away as a priority,” Barker says.
“It was already delayed since the person got tested, so I thought that because [the exposure] was 2 August, I thought it might need to be a priority to go into isolation straight away.”
Across the harbour, on Sydney’s lower north shore, Alex was scrolling Facebook when he came across a post on a local community page, which alerted followers that Coles Gladesville had been an exposure site.
Alex, who asked for his surname not to be used, was there at the same time as the case.
Coles had learned of the exposure on 8 August, but five days later, Alex still hadn’t heard from NSW Health.
“I guess what I was most surprised by was that I just assumed that you check in all your information, I presume it’s going back to Services NSW,” he says. “It just seems that it would be pretty straightforward to automatically send text messages.”
These stories are far from isolated. They are reflective of a contact tracing system under strain from the lightning-fast Delta variant.
Experts say the system is holding up relatively well, given the scale of the outbreak. But compounding delays are starting to creep in at key parts of the complex and difficult task of detecting positive cases, listing exposure sites, and notifying contacts.
“We’ve definitely seen a deterioration but we’re not seeing it in freefall,” Juliette O’Brien, who runs the independent Covid-19 data website, says.
From the very first step in the process, things are taking longer. Pathology companies are increasingly delayed in notifying NSW Health of positive cases, a direct consequence of record levels of testing.
The proportion of locally acquired cases notified to NSW Health by laboratories within one day of specimen collection fell to 78% in the last week of July. That was down from 83% the week prior and 93% in the week ending 26 June.
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The number of positive cases undergoing comprehensive interviews with contact tracers within 24 hours is also slipping, down from 100% at the start of July to 90% in the week to 31 July.
Growing case numbers are forcing contact tracers to conduct shorter, preliminary interviews with the remaining 10%.
There’s also a large number of cases that contact tracers are struggling to resolve.
On average, about 36% of cases in the past week have been “under investigation” with regards to the risk posed by the case – that is, if they were isolating the entire time while infectious, isolating for part of the time or had only low-risk activity in the community, or they were active in the community the entire time.
For both “linked” and “unlinked” cases – that is, whether the case can be traced to a known cluster or other case – about 63% of local cases on average have been reported as under investigation in the daily briefings in the past week.
There have been at least 3,520 cases for which the source of transmission was unknown at the daily briefing since late June. In the more detailed case data that NSW Health publishes online, they often retrospectively update the source of these cases when possible.
Of the 3,520 unknowns, at least 905 were subsequently linked to a known source, as of Thursday.
O’Brien says the proportion of unlinked cases raises critical questions about the NSW outbreak. Contact tracers are clearly not completely overwhelmed. So why are they unable to work out the source of roughly one-third of cases?
“Victoria was an interesting case last year, we all kind of know now that the contact tracing was legitimately overwhelmed, whereas here our contact tracers are still interviewing, in the long interview, 90% of cases,” she says.
“It sounds like they’re not that overwhelmed. So why can’t they solve these cases? That’s the question that I want to know. If they’re not overwhelmed, what is happening?
“And why are we still talking about households and workplaces, when one-third of cases are unlinked?”
Could it be explained by rampant transmission from fleeting contact, making it near-impossible to track? Or are contact tracers simply unable to get to the bottom of the stories they are being told?
‘Found out 10 days after the exposure. Not great!’
In south-west Sydney, Jason was told two weeks ago by an employee at his manufacturing business that the worker had tested positive for Covid-19.
Other staff were asked to get tested and a second case was detected.
Had the employee not told Jason of his test result, work would have continued as normal, potentially allowing further spread.
The first Jason heard from NSW Health was on Tuesday, three days later, despite multiple attempts by him to contact Covid hotlines and health teams over the weekend for guidance on how to respond.
“The real frustration was that had my employee not contacted me … it wouldn’t have then pushed us to tell all our other staff to get tested,” he says. “We wouldn’t have found out about that second case and we would have come in on Monday morning.”
In Campsie, one woman told the ABC she wasn’t notified that she was a close contact until four days after the Campsie shopping centre, where she’d been, was listed as an exposure site.
In Sydney’s northern beaches, the local Manly Daily website is reporting takeaway venues and schools as case locations well before they appear on NSW Health’s website.
Earlier this week, the Guardian asked its readers to share their experiences of contact tracing. Dozens of responses came back, some glowing, but many critical of the delay in notifications.
“Wasn’t contacted [but] was a casual contact, found out through our building putting up signs. Found out 10 days after the exposure. Not great!” one reader wrote.
Another happened to see a NSW Health tweet on 27 July about an exposure site they’d been at, which made them a casual contact.
“I took myself off for a test on 28 July and isolated until I received a negative result on 29 July,” another wrote. “I finally received a text from NSW Health very late on 2 August, that’s 11 days after the potential exposure! At that point, I figured the poor contract tracers had effectively given up on casual contacts.”
The Deakin University epidemiology chair, Prof Catherine Bennett, says tracing systems are never perfect. People often come forward late and with incomplete information, complicating the task of listing sites or alerting contacts.
But Delta punishes delays in a way that previous variants have not, she says.
“All these little weaknesses that aren’t normally a problem, Delta just takes advantage of them,” Bennett told the Guardian.
“If it takes you a bit longer to get to close contacts, they’re going to be infectious because it happens two days sooner, you’ve just got that extra push on. You’ve both got more cases to deal with, that undermines your contact tracing a bit, because you can’t work in the same way, and then that just gives you more cases.”
The data suggests that all close contacts are still being notified within two days of a positive case notification. There is no data for casual contact notifications.
NSW Health does not appear to be suffering from resource constraints. Across its various teams, there are more than 1,000 staff working directly with confirmed Covid-19 cases and contacts.
There is surge capacity of more than 400 staff. That surge capacity is called on whenever demand peaks. Teams from interstate have been brought in. Private contractors are being used.
A spokesperson for NSW Health said delays in interviews were often caused by cases moving to different locations for isolation or healthcare, incorrect contact details, or an inability to reach them by phone.
For the moment, the critical number – the reproduction rate – is still hovering around 1.2, meaning each existing infection causes 1.2 new infections.
That is still enough to cause slow exponential growth, though Bennett says NSW contact tracers have actually performed well to keep the reproduction number at 1.2. “But it still means you’ve got this steady, small growth in cases, which over a week translates into 20% more,” she says.