Two weak positive results for Covid-19 detected in Wellington's wastewater are likely to have come from recently recovered cases continuing to shed the virus, the Ministry of Health says.
In a statement released this afternoon, the Ministry of Health said there was one new case in managed isolation since its last update on Friday.
It said regular wastewater testing was being carried out in Auckland, Wellington, Christchurch, Rotorua, Hamilton and Queenstown and on Friday ESR (Institute of Environmental Science and Research) reported a weak positive test result from a sample taken in Wellington.
A follow-up sample taken yesterday also returned a weak positive result.
"Based on our experience, it is most likely that the two weak positive results are due to recently recovered cases continuing to shed the virus," the ministry said.
"In recent weeks three recovered cases who live in the Wellington region have left the Auckland quarantine facility. A further historical case left a Wellington managed isolation facility the same day the second sample was taken.
"Additionally, it is possible that one or more recently recovered cases from elsewhere could have flown into Wellington."
To help rule out undetected Covid-19 infections, the ministry said anyone with symptoms - especially in the Wellington region - should get tested promptly. This advice also applies to recent visitors to the Wellington region.
There are testing sites in Wellington central, Porirua and the Hutt Valley.
The ministry said further wastewater samples in Wellington were being tested.
Today's single new imported case was a person who arrived from the USA on 10 May.
There were no new cases in managed isolation reported in the last update from the ministry, with just one historical case reported.
There are 19 active cases of the coronavirus in New Zealand and a total of 2290 confirmed cases.
Professor Michael Baker from the University of Otago has welcomed the wider use of wastewater testing as an additional form of Covid-19 surveillance.
He told the Science Media System that it can help detect cases early on before they have grown into large outbreaks.
"A much more important question about wastewater testing is how it is performing in detecting true Covid-19 positive cases in the community, which is the sensitivity of the system."
He said with incidents of community transmission over the last few months, notably the Valentine's Day outbreak in Auckland, it would be helpful to know if wastewater testing had detected these incidents and the timing of the detections.
This information would help determine the likely future role of wastewater testing.
"For example, it may be that we need to invest more resources in this system so that it can perform at the level needed to provide consistent and sensitive early outbreak detection, particularly in the regions where outbreaks are most likely to occur," Professor Baker said.