Wastewater testing up after cases discovered

Wastewater testing for Covid-19 in Nelson and Tasman has been increased in the wake of active cases being found in the community.

On Monday, the first Covid-19 case in the region since 2020 was confirmed, with the tally increasing to 14 as of yesterday.

Up until the week ending November 27 (last Saturday), wastewater testing for Covid-19 carried out by the Institute of Environmental Science and Research had not detected any trace of the virus across Nelson, Richmond and Motueka.

However, ESR senior science leader Dr Brent Gilpin said results from a Nelson wastewater sample collected on November 29 – the same day the first case was announced – had detected the virus. A test in Richmond from November 30 had come back negative.

Gilpin said testing had been increased across the region, to three collections from Nelson, and up to two per week from Richmond and Motueka.

He said further samples collected from Nelson and Motueka were being processed, with the results expected soon.

Gilpin said that while the presence of Covid-19 in Nelson wastewater was an expected result, a positive sample did not always equate to active infections in the community – just as a negative sample did not necessarily mean the virus was absent.

‘‘A positive detection in the wastewater indicates that at least one person has been shedding SARS-CoV-2 into the wastewater in the 24 hours before each sample was collected.

‘‘A positive detection in the wastewater could also be due to a case in a managed isolation facility and/or a non-infectious historical case, or a non-infectious recently recovered case who is still shedding [the virus at] low levels.’’

He said that if there were positive cases in the community, wastewater surveillance would pick them up, with the exception of people who were not connected to reticulated wastewater systems.

Additional factors affecting testing included the level of infection, vaccination state, treatment, and bowel movement frequency, he said.

‘‘We would definitely encourage anyone with symptoms or who has had contact with those outside the area to follow the health advice and get tested.

‘‘It’s best if everyone in the town treats everyone else as potentially infected and takes the appropriate precautions.’’