COVID-19: Wastewater testing

How wastewater testing is being used

Wastewater testing is being used as an extra tool to help monitor for COVID-19 in Aotearoa New Zealand. It is being used as a surveillance tool alongside testing of symptomatic people in the community and asymptomatic testing of workers at the border and in managed isolation and quarantine facilities.

Wastewater is collected from sites that contain a mixture of the wastewater from the toilets, sinks and drains of hundreds of thousands of people in a community. A sample of the water is then tested to see if it contains fragments of SARS-CoV-2 – the virus that causes COVID-19. This allows testing of hundreds of thousands of people for COVID-19 at once.

Any cases of COVID-19 need to be detected quickly in order to stop the virus spreading in our communities. Wastewater testing may be able to give us an early warning of COVID-19 cases in the community. This will help to alert local communities to be more vigilant, keep up hygiene measures, and get tested and stay home if they are unwell.

The risk of infection with COVID-19 from wastewater

There is no risk of infection from the viral fragments in wastewater.

Where wastewater is being tested

Wastewater is currently being sampled at least once a week from many sites around the country, including Wellington, Hamilton, Christchurch, Rotorua, Queenstown and several sites in Auckland. In July, sites in Whangarei, Dunedin, Palmerston North, New Plymouth, Nelson, Taupo, Gisborne, Napier and Invercargill will be added. The Institute of Environmental Research and Science (ESR) tests these samples at their Wellington lab to determine if they can detect SARS-CoV-2.

Detecting SARS-CoV-2 in wastewater

Detecting SARS-CoV-2 in wastewater depends on many different factors, including how many people are shedding the virus in the area, how many people’s wastewater goes into the sampling site and how much the wastewater is diluted. The more people in the area that are shedding virus means, the better chance there is of detecting it. Even if we find no virus in the wastewater, this does not necessarily guarantee an absence of COVID-19 in the community.

People who have an active COVID-19 infection may shed fragments of the virus into the wastewater. Also, people who have recovered from COVID-19 and are no longer infectious may continue to shed fragments of the virus into the wastewater for weeks after they recover. The quantity of viral fragments shed varies between people and over the course of a person’s infection and recovery.

A detection of SARS-CoV-2 in wastewater only tells us that there is one or more active or recovered cases shedding SARS-CoV-2 in an area. It can’t tell us exactly where or who is shedding the virus or how many people are shedding the virus. It can’t tell us if they have an active infection or if they have recovered.

Vaccines do not contain any of the virus that causes COVID-19, or any other live, dead or deactivated viruses so do not result in viral shedding and cannot be detected as viral fragments in wastewater.

How we respond to SARS-CoV-2 detection in wastewater

If SARS-CoV-2 is detected in wastewater the response will depend on what we know about active and recovered cases who live in the area who might be shedding the virus. This might mean increasing how often we do wastewater testing in the area and testing areas close by. Health advice may also be increased, encouraging those who are sick to stay home and get a test, reminders about hygiene and other preventive measures.

If anyone has symptoms consistent with COVID-19, especially if they are in regions who have had COVID-19 detected in wastewater, they should stay at home and promptly call Healthline (0800 358 5453) about getting a test.

Everyone in New Zealand should also continue to use the NZ COVID Tracer app with Bluetooth turned on to keep a record of their movements so they can be recalled quickly if needed by contact tracers.

Also please keep up the hygiene measures that are critical to stopping the spread of the virus – wear a face covering on public transport, wash your hands, and cough or sneeze into your elbow. 

Read more about wastewater testing on the Institute of Environmental Research and Science website

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