Coronavirus: New Plymouth positive wastewater test an 'early warning', but not 'definitive evidence' of community transmission of COVID-19 - Michael Baker

An expert is reassuring New Plymouth residents it's highly unlikely COVID-19 is spreading in the community, despite samples of the city's wastewater testing positive for the virus. 

Two samples tested positive for the traces of the SARS-CoV-2 virus this week, the Ministry of Health said on Friday. 

It's not clear where they came from, with officials suggesting it could be from a recently infected person continuing to shed the virus, but no longer infectious. 

Epidemiologist Michael Baker of the University of Otago says shedding can "go on for many weeks, even months" after an infection, and is "quite likely".

"It's a warning that further investigation is needed," he told Newshub. "One step is to retest the water and see if it's still positive. Then you can think about where people who have left MIQ have gone to, what parts of the country they've returned to and if some of them have tested positive. That's another check to do.

"On its own, it's just an early warning - it's not definitive evidence there is a case in the community… It just means that basically some of the RNA or fragments of the RNA from this virus has been found in wastewater. It obviously is an alert that more investigation is needed." 

The Ministry of Health is looking into whether anyone who tested positive while in managed isolation and quarantine (MIQ) recently went to New Plymouth. The Institute of Environmental Science and Research, which carries out the testing, says it's sensitive enough to pick up even just one person shedding the virus. 

"Obviously the big message to people in the New Plymouth area is if you have any cold or flu symptoms, go and get tested," said Dr Baker, calling community transmission in the northern Taranaki city very unlikely. 

"It's very unlikely... you might have been part of a long chain of transmission in that area, but it is a very low possibility." 

There were a number of positive cases on board a vessel which recently docked in New Plymouth, but the dates and the mariners' activities would appear to rule them out as a source. They had the highly infectious Delta variant of the virus, which Australia has struggled to stamp out after an outbreak that began in June. 

Michael Baker.
Michael Baker. Photo credit: The AM Show

New Zealand paused its travel bubble with Australia on Friday. Dr Baker said it was only a "remote possibility" there is undetected transmission of the Delta variant here. 

"The message is the same - if you have any cold or flu symptoms and you're living in New Plymouth, go and get tested. Or even if you've been in New Plymouth in the last few days, just be extra vigilant - if you have symptoms, go and get tested, ring Healthline and stay at home." 

The ministry says it is setting up additional testing facilities in the city in response. Locations can be found online or by calling Healthline on 0800 358 5453.