Positive Covid cases not reported
Watsewater tests show coronavirus community spread
Covid-19 cases in the Bay of Plenty are being underreported, 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 research institute, 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.
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.
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.
“More data is almost always better.”
Gilpin said wastewater data would help scientists to compare Covid-19 with other diseases such as influenza and respiratory syncytial virus (RSV).
Eventually, Gilpin hoped wastewater results, when studied with other data sources, would be able to measure the number of Covid19 cases that went unreported.
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.
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 Sarscov-2 in both Rotorua and Taupo¯.”
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.”
Kletchko said one other critical reason for reporting was long Covid.
“We know that as many as one in five 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 Covid19 entering the wastewater can be quantified.”
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.”
Miller said reporting positive results was important to help the public health system have an accurate picture of what was going on.
“Self-reported cases generally undercount the true number of cases due to the underreporting of results.”
Miller said maintaining health measures like vaccination, maskwearing and washing hands were also very important.