The family have been isolating since returning from Victoria where they visited Melbourne.

Murrumbidgee Local Health District officials said a 52-year-old woman with mild symptoms was confirmed to have the virus on July 28.

Her son and daughter-in-law, aged in their 20s and their baby have all subsequently tested positive for the virus but are asymptomatic.

Health authorities could not confirm how long the family had been in Melbourne or what the purpose of their visit was, only that they had left NSW since the border closure permit system was introduced.

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The family had a valid permit to cross the border.

Authorities say the family have been self-isolating correctly and that no further contact tracing is required.

Murrumbidgee Local Health District senior environmental health officer Tony Burns said the family had isolated totally.

"We're very confident there's nothing of concern to the general public at this stage," Mr Burns said.

He said the family had been having their groceries delivered and hadn't travelled anywhere else in the city.

MLHD medical director Len Bruce thanked the family for "doing the right thing".

"There should be no stigmatisation involved. That would be the same thing as being angry at someone for catching the common cold," Dr Bruce said.

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