An investigation is under way into how nearly 100 people who tested positive for the coronavirus were wrongly told by text that they were negative.
The people were informed they were in the clear but that their test result was "indeterminate".
Chief Medical Officer Dr Tony Holohan said he only found out about it yesterday and the results appeared to be part of a batch of the backlog of older tests sent to a German lab which should have been given a second reading.
It will be discussed at the meeting of the National Public Health Emergency Team today.
Earlier, HSE chief Paul Reid said the mistake, which happened on Saturday, was under investigation.
The people involved would have been asked to self-isolate from the point at which they were referred for a test.
It is unclear if they had all recovered when wrongly given the all-clear on Saturday and whether they would have come out of self-isolation, which could have caused them to pass on the virus.
The HSE confirmed a large group of people who were positive for the coronavirus were incorrectly contacted by text and told they were negative.
On Saturday "less than 100 people had been advised, in error, that their test did not detect Covid-19. On review these patients were, in fact, positive for Covid-19", said an HSE official.
"This error occurred because, in the case of a small number of lab tests, the initial test result was indeterminate.
"Ordinarily, such results would indicate that another test is required.
"Given that we are dealing with a pandemic and that it was not possible to request another sample in the required time-frame a decision was made to review the initial test results and retest the sample.
"This was done to maximise the chance of getting a test result for the patient if possible.
"The National Virus Reference Laboratory reviewed the detailed test data from the original test result and retested the original sample."
As a result they were able to make a determination that some were, in fact, "weakly positive".
"Unfortunately, these indeterminate cases were initially reported as not detected and consequently were notified to people as such in line with the results communication process.
"This was picked up by our contact tracing team and remedial action taken immediately.
"A team of public health clinicians has contacted or attempted to contact each of the people involved to advise them of the correct outcome of their test, and to provide the appropriate public health advice and support to them.
"We are satisfied that no other patient has been impacted by this error.
"The HSE apologises for this error, and every effort has been made to ensure that the correct information is communicated to these patients without delay," the spokeswoman said.
It comes as Mr Reid said the backlog of 11,000 tests - down from 35,000 - will be cleared by the end of this week with most of the analysis carried out by a laboratory in Germany.
One in five tests in the backlog will be read here in over 20 labs and in hospitals. But Mr Reid said the testing regime is being ramped up with the use of more laboratories including Enfer.
The average daily number of tests is 2,800 so far, but this rose to 7,800 over the weekend.
Around 500 people have appointments to provide a swab sample scheduled. Overall, 72,000 tests for the coronavirus have been completed here since the crisis began.
Some 500 people are being contacted daily with their test results by doctors.
As of last week, the average contacts a newly diagnosed person with the virus had was three.
It is expected that from next week more people, outside current priority groups, will be offered a test.
But there is still uncertainty over the future volume of testing here because it is unclear if the German lab will continue to take outsourced tests.
The continued adequate supply of a reagent necessary to carry out analysis cannot be fully guaranteed, Mr Reid said.
Meanwhile, Dr Colm Henry of the HSE said figures indicate that 64 patients have been discharged from critical care after being admitted due to serious complications from the coronavirus.
Sadly, 35 patients have died in intensive care, he added.
"We saw Prime Minister Boris Johnson say that his time in critical care could have gone either way. It could have. It is a peculiar illness.
"Most of the patients who went to intensive care here are still there but there also patients leaving critical care. It is a tribute to our staff, who are world class."
It can take seven nurses to staff an intensive-care bed, which is very labour intensive.The HSE has offered contracts to 1,100 staff who answered its recent recruitment drive.