Millions of Melburnians are being urged to monitor for symptoms of COVID-19 after viral fragments were detected in a “large wastewater catchment” that services the city’s northern, western and eastern suburbs.

Over five million people live in Melbourne and around three million of those reside in those areas.

Traces of COVID-19 have also been detected in another wastewater catchment in Melbourne’s southeast.

The Department of Health released a statement saying the “unexpected detections” could be due to a person or persons with the virus being in the early active infectious phase.

Or it could be because they were continuing to shed the virus after the infectious period, they said.

“While it is possible that these detections are due to a visitor or visitors to these areas who are not infectious, a cautious approach is being taken,” the statement read.

People who live in or have visited the following areas should monitor for COVID-19 symptoms and get tested if any develop:

  • North, west and eastern suburbs from 4 to 12 April. This detection is in a very large catchment that services suburbs stretching from Melbourne’s northwest to the outer northeast.
  • Cranbourne and surrounding suburbs from 6 to 12 April

The two new detections come after people residing in 16 suburbs were issued a warning earlier in the week about similar wastewater discoveries.“Coronavirus fragments have been detected in wastewater from the Ringwood area,” the Victorian Department of Health said in a statement just before 6 pm on Tuesday.

The east Melbourne suburbs affected include Bayswater, Bayswater North, Boronia, Croydon, Croydon North, Croydon South, Heathmont, Kilsyth, Kilsyth South, Montrose, Ringwood, Ringwood East, Sassafras, The Basin, Tremont and Wantirna.

This article originally appeared on Over60.