Over the past year, health districts across the state have been working with local councils to test sewage for any traces of COVID-19. This is done to help track any infections in the community, and to provide early warning signs of an outbreak - or increase - of infection.
To date, there have been no traces of COVID found in Wagga sewage.
High levels of COVID were recently detected in sewage in the Newcastle and Hunter region, where a number of cases have since been identified, and traces of the virus were also detected in Armidale sewage, with two cases announced in that region on Saturday.
These sewage detections, and subsequent cases, have lead to concerns about the virus leaving Sydney and spreading to regional NSW.
MLHD director of public health, Tracey Oakman, said that sewage surveillance testing has been carried out in the Murrumbidgee region for 12 months at sites in Albury, Deniliquin, Griffith, Gundagai, Hay, Moama and Wagga.
"The NSW Health sewage surveillance steering committee regularly reviews the sewage sampling program and tailors it to the needs of the public health response to COVID-19," she added.
"To date, there have been no positive samples detected in MLHD."
How does testing work?
The state's sewage surveillance program tests untreated sewage for fragments of COVID-19 at treatment plant locations across NSW.
A NSW Health spokesperson explained that fragments of COVID-19 can enter sewage through an infected person's faeces, and also when washed off hands and bodies via sinks and showers.
"Within the chosen sewage catchment areas, researchers collect samples of wastewater at the inlet of the treatment plant, before it goes through the treatment process," the spokesperson added.
"The samples are then analysed with a specialised test that looks for fragments of the virus".
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The spokesperson also said that testing raw sewage for COVID is a specialised test that not all laboratories can undertake.
"Sewage must be filtered and processed before the laboratory looks for genetic material," they said, using a process called polymerase chain reaction (PCR).
PCR is a laboratory technique used to amplify DNA sequences, in which the temperature of the sample is repeatedly raised and lowered to help a DNA replication enzyme copy the targeted DNA sequence.
Why test sewage?
A NSW Health spokesperson said that surveillance testing of sewage can help track infections in the community, provide early warning signs and "potentially give an estimate of undetected infections in the community."
The tests provide data to NSW Health to assist with its COVID-19 response measures.
The spokesperson also said that locations for sampling must be prioritised, with locations of concern identified by risk factors, tourism, borders and other issues which may affect how the virus is travelling through NSW.
Does finding traces of COVID in sewage mean the virus is in the community?
There are several different reasons why traces of COVID could be in sewage, the NSW Health spokesperson said.
"It could mean there has been one or more people who are infectious with COVID-19 in the catchment area," they said.
"It could also mean that there has been one or more people in the catchment area who have recently recovered and are no longer infectious."
The spokesperson said that those recently recovered from COVID can sometimes continue to shed virus fragments for several weeks "even if they are no longer infectious".
"It could also mean that a person with COVID-19 might have visited the community and has since left the area," the spokesperson added.
What would happen if traces of the virus were detected locally?
An MLHD spokesperson said that if traces of the virus were detected in the region, the MLHD would notify the community, ramp up testing in that area, and deploy additional testing resources - such as the mobile testing clinic - if necessary.
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