66-year-old Maria McBirney (Ngāpuhi, Tainui, Kūki Āirani) caught Covid in March. Video / Whakaata Māori
Covid-19 cases in the Bay of Plenty are being under-reported, according to recently released wastewater data.
And local experts agree a lack of self-reporting could lead to an undercount of the virus' spread in the community.
The Institute of Environmental Science and Research, or ESR, a New Zealand Crown researchinstitute, has released data showing the level of Covid-19 in the region's wastewater does not correspond with the number of cases recorded.
Most of ESR's samples are collected by an autosampler, which collects a small volume of wastewater at regular intervals over the course of a 24-hour period.
Wastewater samples are then sent from local plants to ESR for testing.
When enough of the virus is in the sample to quantitate, scientists convert that to a viral load of genome copies per day, per person.
ESR's online Covid-19 wastewater dashboard, which went live last week, enables Kiwis to check the quantities of Sars-CoV-2 (Covid-19) scientists are finding in their region and then compare that to case numbers reported each day.
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ESR science leader Dr Brent Gilpin said analysing the trends of wastewater test results over time helped modellers to better understand the spread of Covid-19 in the community.
Gilpin said wastewater data would help scientists to compare Covid-19 with other diseases such as influenza and RSV.
Eventually, Gilpin hoped wastewater results, when studied with other data sources, would be able to measure the number of Covid-19 cases that went unreported.
"It's a non-invasive way to objectively measure what the true spread is."
The number of Covid-19 community cases continues to rise across the country.
On Monday the Ministry of Health recorded 396 new cases in the Bay of Plenty and 223 in the Lakes District.
In the past seven days, an average of 17 deaths have been confirmed each day as attributable to Covid-19.
ESR researchers test wastewater samples at the Covid-19 testing facility in Porirua. Photo / NZME
Te Whatu Ora Lakes quality, risk and clinical governance director Dr Sharon Kletchko said ESR shared their results with the district weekly.
"They have been vital in terms of alerting us to the prevalence of Sars-CoV-2 in both Rotorua and Taupō."
Kletchko said ESR's findings helped to inform the public health response but under-reporting had an effect.
"We know that a number of people who test positive fail to report they are positive," Kletchko said.
"For us to better understand how much Covid is in our community every person who tests positive should report."
Wastewater samples collected for analysis at the ESR laboratory in Wellington. Photo / Supplied
Kletchko said one other critical reason for reporting was long Covid.
"We know that as many as 1 in 5 persons contract what is called long Covid.
"This is a condition where symptoms, some very debilitating, continue for months after the acute episode of the infection.
"Having the positive test reported is added to the individual's health record and assists with accessing medicines and treatments that could help them."
Toi Te Ora Public Health medical officer Dr Jim Miller said while wastewater testing could not measure the exact number of cases in an area, the process could reveal two things:
"Firstly, whether there are any fragments of Covid-19 in the sewerage of a settlement or township. This is very sensitive and can pick up a single infection in the area.
"Secondly, the testing can give an idea of the size of the local outbreak and, importantly, whether it is rising or falling, since the amount of Covid-19 entering the wastewater can be quantified."
Toi Te Ora Public Health medical officer Dr Jim Miller. Photo / NZME
Miller said Covid-19 infections were widespread in all communities so wastewater testing was only one of the indicators being used to understand the size and impact of the virus across the country.
"[Other indicators are] PCR tests done in hospitals, self-RAT testing and reporting in the community, visits to primary care, calls to Healthline and admissions to hospital.
"Taken together, these can help to estimate the true size of the outbreak, indicate where cases are trending, and modelling can provide scenarios that help future planning."
