Wastewater testing of covid-19 is becoming increasingly important as individual testing dwindles.
Covid-19 in wastewater is monitored by the Institute of Environmental Science and Research [ESR]. It published results on the prevalence of the virus and the most common variants in the community.
Masterton-based epidemiologist Roger Morris said the Ministry of Health’s recording of cases via RAT and PCR tests was reliable a year ago, but that was no longer the case.
“When individual testing and reporting was high [during the pandemic’s peak] last year, it matched very closely with the amount of covid in the wastewater.
“The ESR dashboard shows the Wellington region is not individually testing nearly as much this year as they were between March and November last year.
“Individual reporting was far more accurate, but as people stopped reporting their results at the end of last year, Wellington wastewater has a higher rate of cases than individual reporting.”
However, Morris said there was a close correlation between the two data sets.
Morris said he was impressed by how accurate the covid-19 wastewater detection was since the wastewater surveillance
first started in late 2020,
“The overall value of wastewater testing is surprisingly good.
“Wastewater testing can not only detect that there is covid in the population, but it detects even small amounts of the virus. If five to 10 people in the population get covid, it will show up in the wastewater surveillance.”
He said the surveillance works well for covid-19 but wasn’t effective for all viruses, as it depended on how human bodies excrete it.
“Covid-19 appears in wastewater because it’s excreted through faeces and urine. And there’s enough of that virus excretes that it appears quite clearly in the testing.”
“Some respiratory viruses are only excreted from the lungs, not faeces or urine, so they don’t appear in wastewater. “
ESR uses a Quantitative RT-PCR to test the prevalence of covid-19 in the community. The testing is done quantitatively, meaning it measures the amount of RNA from the the spike protein, and from there can work out how much viral RNA is in the wastewater.
In Wairarapa, according to the wastewater, covid-19 had increased in Featherston, Greytown and Masterton, but decreased in Martinborough compared to the previous week, as of February 12. Carterton reported no change.
The most prevalent covid-19 variants as of February 12 were CH1.1, followed by BA2.75, XBB and XBC.
