But the testing of raw sewage from Dubbo Sewage Treatment Plant for molecular markers of SARS-CoV-2, the virus which causes COVID-19, has not yet required the issuing of a public health alert.

"There have been no detections of COVID-19 in Dubbo sewage," a health district spokeswoman said.

READ ALSO:

Dubbo was selected to be part of the NSW Sewage Surveillance Program, launched in July.

Under the program, samples of untreated sewage are tested at treatment plants across NSW.

On four occasions to date the program detected remnants of the virus in locations where there were no known recent cases of COVID-19.

The four locations are the Snowy Mountains, West Camden, North Richmond and Bathurst.

On October 21, NSW Health advised of "remnants of the COVID-19 virus" being detected in Bathurst's raw sewage.

It asked people who attended the Bathurst 1000 motor race the previous weekend and residents of the city with respiratory symptoms to get tested for COVID-19 immediately.

"An infected person can shed virus in their faeces even if they do not have any symptoms, and shedding can continue for several weeks after they are no longer infectious," the health district spokeswoman said.

NSW Health calls the program "another tool in the fight against the global pandemic".

There is no evidence COVID-19 is transmitted via wastewater systems, it says.