With two new cases confirmed, the COVID outbreak in the Northern Territory is currently standing at 25.
A key piece of the puzzle emerged late on Thursday, when it was confirmed that the cases recorded in the small community of Robinson River and Katherine this week are linked to the Darwin/Katherine outbreak from nine days ago.
But the genomic testing that confirms that link doesn't explain when or how the transmission occurred.
"In a sense, that just makes this mystery even stranger because we still don't know how it went from that small first cluster to no cases for nine days," NT Chief Minister Michael Gunner said.
That means there is "a very real possibility" there are people with COVID in Katherine who don't know it, Mr Gunner said.
Here are the new testing rules announced on Friday.
New testing rules now in place
People currently displaying symptoms of COVID-19 have always been urged to get tested, as have close or casual contacts or anyone who has visited an exposure site.
But from Friday, anyone who has shown symptoms at any time in the past few weeks is being asked to get checked.
Also, anyone who has already been tested as part of the current cluster, or who is a close or casual contact, or who has visited an exposure site, is being asked to get re-tested, regardless of whether they're showing symptoms.
"We know that people can test negative for Delta initially, only for it to pop up a few days later," Mr Gunner said.
"In fact, one of the first cases in this second cluster had that happen to him — it was his second test that discovered the infection.”
Mr Gunner said household contacts of anyone who falls into the above categories should also get tested.
"I know the lines are long, I'm sorry about that,” he said.
Testing to get underway in Binjari
Authorities are also focused on testing in Binjari, an Aboriginal community of about 200 people on the outskirts of Katherine.
A wastewater sample in the community came back positive for COVID late on Thursday.
A "rapid assessment team" has been deployed to test and vaccinate residents, with support from the Katherine-based Wurli Wurlinjang Aboriginal Health Service.
"It is our intention to test every single person in the Binjari community today," Mr Gunner said on Friday.
"And we will also get more people vaccinated there today."
NLC demands expansion of rapid antigen tests
From Friday, anyone who travels from a major urban centre to a remote community with a first-dose vaccination rate of less than 70 per cent must get a rapid antigen test 72 hours before travelling and return a negative result.
But the Northern Land Council said the rule should be expanded to include any remote community, not just those with low vaccination rates.
"We want you to do a rapid antigen test regardless of the vaccination rate because we want to do everything we can to protect our communities," NLC chairman Samuel Bush-Blanasi said.
"Wait until you get that negative result before you travel."
The NLC is also urging all Territorians to stop travel to or from Aboriginal communities "unless it is absolutely necessary", to prevent the spread of COVID-19 to other communities.
