Covid-19 should be stalked suburb-by-suburb in Auckland, using wastewater testing, a public health academic says. David Williams reports
Once he’d dispensed his reassuring take on the continued low daily case numbers in the Delta outbreak, Director-General of Health Ashley Bloomfield adopted a headmasterly tone.
On Sunday there were 4750 Covid-19 swabs processed around the country, with just over 2000 taken in metropolitan Auckland. “This is the lowest testing day since the start of the current community outbreak,” Bloomfield said at yesterday’s post-Cabinet briefing.
In large part, this reflects a decrease in people with symptoms. Indeed, NZ’s Flu Tracker shows the dampening effect, like last year, of Alert Level 4 on all respiratory illnesses.
Also, fewer new locations of interest are emerging from new Covid cases.
“However,” Bloomfield began, with a grimace, “testing remains central to us being confident that the outbreak is under control. Our most important message today is if you have any symptoms you must get tested, wherever you are in New Zealand.”
The most important thing is getting tested if you’re symptomatic, he said – “everything else is supplementary”.
Laboratory testing data, broken down by district health board area, show Counties-Manakau was the only DHB to remain above 1000 tests on Sunday.
Beyond Auckland, only four DHBs – Canterbury, Capital and Coast, Taranaki and Waikato – were above 100 tests.
The Ministry of Health figures reveal Sunday’s total of community tests processed was 3829, compared with 15,065 the previous Sunday.
(The data are for community tests processed and reported by laboratories, which are coordinated nationally and reported daily by the Ministry of Health. They do not include tests taken from border workers or managed isolation or returnees in managed isolation of quarantine facilities. The figures are reported by DHB of residence, based on a person’s national health index.)
Prime Minister Jacinda Ardern joined Bloomfield’s testing theme from the podium yesterday. She said unlinked or mystery cases are still emerging, making it unclear if undiscovered chains of transmission are washing around the community. That’s why testing’s so important.
“It doesn’t matter where you are in the country, we need you to be tested,” Ardern said.
Professor of public health at University of Otago Wellington, Nick Wilson, agrees low community testing in Auckland is concerning. But he believes the Health Ministry needs to change its testing approach, exploiting wastewater testing more as an early detection tool.
“They haven’t got the balance right, scientifically,” he says. “We have this valuable tool which has been getting better and better: wastewater testing.”
Crown research institute ESR has been doing a fantastic job of scaling up wastewater testing, Wilson says. By last Thursday, testing had extended to 148 locations – 98 in the North Island and 50 in the South – covering around 3.8 million people.
But Wilson says given the current outbreak is in Auckland, ESR should potentially reduce some South Island testing and put all its effort into getting the outbreak under control in Auckland.
“We need to really put enormous effort into helping Auckland,” Wilson says.
He’d like to see wastewater testing ratcheted up to the suburb level in Auckland.
“You identify a suburb, just like Warkworth was identified with wastewater testing, and then you hone in. You encourage not just people with symptoms in that affected area but anyone to go for a test, and then you can find the last cases that are out in the community by this combination of wastewater testing then targeted community testing.”
A study published last month in mSystems, a journal of the American Society for Microbiology, said 68 automated wastewater samplers at a California university led to the early diagnosis of nearly 85 percent of all Covid-19 cases on campus, “thereby averting potential outbreaks”.
Wilson says once positive samples of Covid-19 are identified in Auckland suburbs, testing can be done further along the wastewater system. “You can actually find within a city block where there are cases.”
Community testing is important, Wilson says, noting the millions of dollars a day being spent on testing stations is a drop in the bucket compared to the expense of lockdowns. But another argument for rolling out greater wastewater testing is the lower cost – he estimates about 1 percent of community testing.
“This is amazing technology,” he says. “I don’t think people quite realise that if you have symptoms and you touch your nose or your mouth, there’ll be viruses on your hand. When you wash your hand that virus goes into the wastewater system and that can be detected.”
Daily testing needed
Wilson disagrees with the Government’s approach in other ways.
At yesterday’s briefing, Bloomfield described the methods his ministry will use to improve confidence that cases aren’t going undetected in Auckland, and to protect the rest of the country from what he called “leakage”.
Part of the bundle of measures, spanning the next two weeks, is more regular surveillance testing for Auckland hospital workers and twice-weekly testing for staff in quarantine facilities.
“They should have been tested daily from about a year ago, with saliva tests and then rapid antigen tests as well,” Wilson says. “It’s just astounding how they don’t take these things seriously, given the downside costs.”
He also thinks the MIQ system needs an overhaul, with dedicated facilities outside of Auckland. “That’s just so obvious – it’s absurd that they’re just continuing this not-fit-for-purpose model.”
From midnight tomorrow, parts of the country outside Auckland will move to alert Level 2 “Delta”, which mandates mask-wearing in most indoor spaces, and restricts public gatherings, including at bars and restaurants.
“They’ve done a great job on extending masking and QR code scanning and tighter restrictions on indoor settings, but we would have liked those all to be tighter,” Wilson says.
Exempting schools and universities from a mask mandate is muddling the public message, he says. “It’s such a simple message – masks indoors everywhere except the home.”
Wilson thinks allowing large venues like bars, nightclubs, and churches at a Level 2 “plus” is a mistake.
How long might Auckland stay in Level 4? Wilson’s best guess is another week, given the encouraging, overall downward trend. But he’s concerned about a positive case who shared a Middlemore Hospital surgical ward with three other people.
“If that’s connected to an essential worker who has then infected other essential workers you could have a super-spreading event in a factory where everyone’s still working. That could take another two weeks at alert Level 4 to sort out.”
Testing locations can be found at the Healthpoint website, while the Ministry of Health lists locations of interest.
Those who were at a location of interest at relevant times, or who have cold or flu symptoms, should call Healthline: 0800 358 5453
