A senior nurse who recently returned from coronavirus-hit Victoria has become South Australia's latest positive case, as the state mulls a "soft border" with Queensland.
The woman, among a group of nurses sent to Victoria to assist in the embattled aged-care sector, flew into Adelaide on Friday and remains in hotel quarantine.
She hasn't shown any COVID-19 symptoms and is well.
"It really just shows that even with our very most experienced nursing staff and wearing all of the PPE required that this is a very transmissible virus," Chief Public Health Officer Nicola Spurrier said on Sunday.
"I think it also reflects the fact that our nursing homes are an even more difficult situation than in our hospitals."
The group was serving a two-week stint as part of a staggered response but stayed for an additional week.
She flew back to SA with eight colleagues, all of whom were deemed close contacts but already in mandatory hotel quarantine.
There are now three active cases in South Australia.
With Queensland recording another two cases linked to a youth detention centre cluster, SA Health is urging people to reconsider travelling to Greater Brisbane and Ipswich.
Dr Spurrier described the situation in Queensland as "fluid" and "very concerning" and said officials would consider introducing a soft border with Queensland, forcing returned travellers to quarantine.
"We do have open borders with Queensland and there are quite a significant number of South Australians coming back from Queensland every day," Dr Spurrier said.
An alert was issued on Sunday for 40 venues, mainly south of Brisbane, visited by people linked to Queensland's new outbreak.
Dr Spurrier urged returned travellers from the Sunshine State who had attended any of the locations to self-isolate for 14 days and monitor for symptoms.
South Australian Premier Steven Marshall recently returned from a trip to Queensland and has since tested negative.