Stay-at-home orders for the Oberon LGA were introduced from 6pm on Wednesday and apply to anyone who has been in that area since September 20.

On the same day that another 12 cases were announced for the LGA, a likely source of how the outbreak began was also revealed.

Speaking to media on Thursday, Western NSW LHD chief executive, Scott McLachlan, said they believed it originated from Sydney.

"So people who travelled to Sydney for whatever reason and brought it back to Oberon," he said of the source.

"We know that the sewage detections have been going on for some time and there's potentially multiple sources in Oberon and so there's the real signal there with Oberon going back into stay at home orders, we've got a window of time to get on top of the outbreak.

In total there were 43 more cases recorded up to 8pm Wednesday night, with Mr McLachlan adding that there were a "significant" number of cases that came in overnight that will be added to the next day's totals.

"We have once again seen a significant increase in cases overnight," he said.

"Our teams are still working through those, but more cases in Wellington - a substantial amount in Wellington - Narromine, Cowra and Oberon."