The Vermont area includes Balwyn, Balwyn North, Blackburn, Blackburn, North, Box Hill, Box Hill North, Bulleen, Doncaster, Doncaster East, Donvale, Mitcham, Mont Albert, Mont Albert North and Nunawading.
The CHO email said the matter could be someone shedding the virus who is no longer infectious or it could be someone who is infectious but undiagnosed.
Yesterday the wastewater testing found traces in the Bendigo area which takes in California Gully, Eaglehawk, Epsom, Huntly, Jackass Flat, Maiden Gully, Marong, North Bendigo and Sailors Gully.
Anyone who was in those suburbs from June 3-7 should get tested if they have any symptoms.
You can read more about the wastewater testing results here.