Wastewater more reliable: prof
University of Otago epidemiologist Michael Baker. Photo: file
With another wave of Covid-19 on the horizon, wastewater testing has become a more reliable sign of community infection than self-reporting, a Dunedin expert has said.
University of Otago epidemiologist Michael Baker said since last week, wastewater testing in Dunedin and across the country showed a "consistent sharp spike" in detection of SARS-CoV-2, or the Covid-19 virus.
"This rise suggests we are seeing the beginning of a new wave of Covid-19 infection across New Zealand."
In the past week, the Southern district recorded 96 new cases of Covid-19, tied for second-most in the country with Canterbury and behind Waitematā (141).
However, an apparent strong decrease in testing and self-reporting across New Zealand meant wastewater was a more useful indication of infection in the community, Prof Baker said.
"A lot more people will be walking around not knowing they've got the infection and not able to take preventive measures to infect other people.
"So it has weakened our support for preventing transmission."
Otago Primary Principals' Association president Kim Blackwood said while schools were seeing plenty of general illness, few cases were confirmed to be Covid-19.
"They've got one or two cases, but it's not impacting majorly at this point."
As Covid-19 tests were no longer free, "the question that has to be asked is whether people are testing".
"Because I'm not sure that they are."
Prof Baker appeared to agree.
Removing government support for Covid-related sick leave in 2023 contributed to a "sharp drop" in testing.
"That's when the wastewater [virus detection] line stayed fairly high, and the self-reported line started to dip.
"And then, of course, a year later, we removed the free [rapid antigen tests], and I think there was also an even bigger divergence between those two lines."
While it appeared another Covid-19 wave was emerging "we don't know how big or how prolonged it'll be", Prof Baker said.
Now was the time for people to get a booster vaccine, "particularly if you're over 65 or have underlying illnesses, or pregnant".
Recent hospitalisations due to Covid-19 were not immediately available.
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