The source of at least one COVID-19 case in the Eurobodalla Shire remains a mystery, despite the best efforts of medical bloodhounds.
The trio of fresh cases identified on August 10 and 11 was positively linked to a case at the Batemans Bay Soldiers Club, identified on July 18.
Southern Director of Public Health, Tracey Oakman, told Australian Community Media "a distinct link was determined".
"The contact tracers at the public health unit have absolute confidence that there was a link," Ms Oakman said.
"The cases are doing as directed by the health department in terms of isolation."
Three shire residents were among eight cases associated with the club in July: a staff member and two patrons, one of whom had visited Club Malua and Club Narooma the previous week.
Ms Oakman said blood testing in the weeks after a patient tested positive could sometimes help researchers determine which strain of COVID-19 was involved and therefore track its source and spread.
However, no source of infection has yet been determined for the patron who had visited the three clubs.
"We have been unable to identify a source of infection for this person," Ms Oakman said.
However the staff member's case "was genomically linked" to the Sydney family who visited the club on Monday, July 13.
That family and their close contact were shown to have the same strain of the virus circulating in Sydney before their arrival in Batemans Bay.
Ms Oakman said blood testing was not a good early test, because it could take five to seven days for the virus to show up.
However, as time elapsed, patterns could emerge: "In that five days to three weeks after contracting, your immune system has changes. The blood test can give some general idea about where (you are) in the course of the illness, but it is not 100 per cent definitive. Some will respond differently. It is only a guide."
Blood tests can help know when someone was infected - which helps contact tracers widen their net.
Despite a slew of tests since Monday, August 10, no fresh cases of COVID-19 had been detected in the Eurobodalla Shire by late Thursday afternoon.
Residents and health authorities were hoping the run of negative results would carry on, but public health officials continued to call for vigilance.
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