A COVID-19 test result that is a “weak positive” is not a “false positive”, Ministry of Health CEO Dr Siale ‘Akau’ola confirmed to Matangi Tonga today. He was responding to public comments regarding the meaning of the test results from Tonga's first COVID case.

A “weak positive” result means a very small amount of the virus is picked up in the sample that has been tested.

This is not the same as a “false positive”, he said, “when a test turns out positive due to other conditions or other viral particles which are not COVID-19 viral particles. This can happen in test procedures which are not specific enough for Covid-19.”

This means a person who tests false positive does not have the disease.

Last Friday, Tonga recorded its first case of COVID-19 when a person tested weak positive after arriving on a repatriation flight from Christchurch on Wednesday, October 27.

“We are confident that it is not false positive since the machine has picked up viral particles in the sample,“ said Dr ‘Akau’ola.

“It is a weak positive since viral particles picked up were low in level. Shown by CT level and we repeated the test - three times.”

The CT level is the cycle threshold level, which indicates how much virus an infected person has. And it depends on analyser set levels for positive and negative.

“The first positive test was picked up in the pooled sample of four samples, tested once again on individual samples of the four pooled samples, which identified the index case; and again on repeated sampling from the index case, which was identified in the first sample. This is technical stuff but we want to ensure people understand the nature of the test.”

“The test procedure we use in Tonga is very specific for COVID-19 and we don't expect false positive,” he said.

The person tested negative for COVID-19 in a second test done on Monday, November 1, and another test will be done at the end of this week.

Meanwhile, Tonga is currently on lockdown with extended curfews and social distancing enforced as a precaution, for a week until Monday, November 8. Shops selling foodstuffs remain open along with essential services.

New Zealand

Meanwhile, the chief executive of the New Zealand Ministry of Health, Dr Ashley Bloomfield, told a media conference yesterday that they did not expect to receive samples of the case that had travelled from Christchurch to Tonga.

“No, we don’t have that back, and I think it’s unlikely we will,” he said. “and our experience is that there’s very little viral—there’s not enough viral material there from the sample to be able to get a whole genome sequence.”