The Canterbury Regional Health Authority fears up to half of Covid-19 cases go unreported as new data shows a growing gap between cases and virus fragments in wastewater.
On Friday, Crown Research Institute of Environmental Science and Research (ESR) launched a interactive Covid-19 wastewater dashboard to share how the virus tracked across New Zealand.
The dashboard allows users to monitor how much Covid-19 is in wastewater in different regions, compare it to reported cases, and see if the levels are increasing or decreasing over time.
ESR science leader Brent Gilpin said a key trend they noted was a “growing gap” between reported cases and the amount of Covid-19 virus in wastewater.
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On Monday interim Waitaha/Canterbury district director for Te Whatu Ora (Health NZ) expressed concern in their newsletter they could underestimate current Covid-19 cases by half, based on the new wastewater data.
This came when the department revealed that there were 169 people in Canterbury hospitals with the virus – the highest number since the start of the pandemic.
That meant one in five about 836 people currently hospitalized with Covid-19 were in Canterbury, despite the district making up only about a tenth of the population.
However, when reported cases of Covid-19 and wastewater levels on a national level were compared, the numbers were quite similar.
ESR
The nationwide trend for Covid-19 reported case numbers versus virus particles in wastewater.
Gilpin believed wastewater data would eventually provide an accurate measure of Covid-19 in the community, similar to how it was used to measure drug use.
“Over time, fewer and fewer people will use rapid antigen tests,” he said.
Gilpin said to get the data, they collected wastewater samples from different watersheds and extracted viral RNA from them.
They then used that to calculate genome copies per liter of wastewater, multiplied by liters per day going into that watershed, divided by the number of people living there.
But accurately measuring how viral RNA levels in wastewater equated to actual cases was still a work in progress.
People can lose billions of particles or they can lose very few, he said, and it often varied over the course of their illness.
ESR/included
ESR has tested wastewater samples across the country for the Covid-19 virus. (File photo)
It was something Kiwi researchers worked with their foreign counterparts to better understand.
Gilpin said they were also able to see which variants of the virus were spreading the most in communities.
Five weeks ago, Omicron sub variant BA.2 was the most common in the country, while sub variant BA.4/5 accounted for about 10% of the cases. Now it was 75%, he said.
The amount of Covid-19 in wastewater started to skyrocket around February, in line with The Exponential Spread of Omicron Across New Zealand – with case numbers exceeding 20,000 per day at the peak of the wave.
ESR
Canterbury’s trend for Covid-19 reported case numbers versus virus particles in wastewater.
Wastewater levels had peaked around March and Gilpin said that, like reported case numbers, they had fallen slightly since then.
“It hasn’t gone down as much as I think we’d hoped… as we go forward hopefully we’ll see the levels in wastewater start to drop.
“Levels in Auckland peaked much earlier than in the rest of the country, as Covid was circulating there much earlier.”
Seeing the level of the South Island peak moments later, they had converged over most of the country.
In central Auckland, genome copies per person, per day were slightly lower than in some regions, he said, but “certainly not the difference seen last year”.
ESR
Auckland’s trend for Covid-19 reported case numbers versus virus particles in wastewater.
Gilpin said the wastewater data could provide confidence that any drop in Covid-19 cases was real, rather than just the result of fewer people testing.
This was just the first version of the wastewater tool, and Gilpin said they hoped to eventually be able to use it to provide more in-depth data on potentially even more infectious diseases.
It was important to make sure the data itself was available for both the public and fellow researchers to use and analyze, he said.
“This is the way public health needs to move forward … so that people can make their own decisions.”
In addition to crowdsourcing a combined truth, Gilpin said it could help “overcome the challenges of disinformation itself.”