While positive samples have been expected at sewage testing sites because of the prevalence of COVID-19 cases in Victoria, the Apollo Bay result is of interest because there have been no known cases in the coastal town in recent weeks.

The preliminary result does not necessarily mean there are active cases of COVID-19 in Apollo Bay. Testing of the entire water network had been increased as a precaution, Professor Sutton said.

One reason the sample might have tested positive was that it had been shed by people who had travelled through the coastal town from neighbouring areas, he said.

It can take several weeks for someone to stop shedding the virus and further analysis is required to assess the significance of the preliminary result. The fragments themselves are not infectious.

The test result may also be a result of someone with COVID-19 who hasn’t been detected through testing.

“Finding cases early can help our disease detectives track the spread of the virus and implement strategies to minimise transmission, preventing hotspots or clusters before they have time to develop,” Professor Sutton said.

“Until we have a highly effective and available vaccine, early detection and prevention are the keys to combating coronavirus.”

The department is analysing sewage for fragments of coronavirus at sites across Victoria as part of a national research program.

Earlier this year, project manager Dan Deere, who has been hired by Water Research Australia, told The Age testing sewage for viruses was not new with periodic monitoring for polio over many decades.

“We know we can test sewage and find diseases,” he said. “The problem in this case is that this is a new virus and the methods for testing for it haven’t been through the usual rigour.”

Dr Deere said once a reliable test was in place, along with the know-how to use it most effectively, the team could move to “phase three” of their task – “routine surveillance”.

The science could also be used to detect COVID-19 in small enclosed environments such as planes and cruise ships.

“Wastewater testing provides an additional and complementary tool to the existing public health response and can provide early warning that coronavirus is in a community before traditional testing methods,” Professor Sutton said.

Wastewater is treated to kill a wide variety of micro-organisms, including viruses, before it is returned to the environment, the department said.

There is no impact on the local water supply which is safe to drink.

There are 25 sampling sites across Victoria including at Melbourne’s Eastern and Western Treatment plants and 11 other sites including along the Mornington Peninsula and regional sewage treatment plants at Ararat, Ballarat, Bendigo, Colac, Geelong, Moe, Mt Martha, Shepparton, Sunbury, Traralgon, Warragul and Wonthaggi.

Melissa Cunningham is The Age’s health reporter.

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