The HSE chief executive says an increasing number of people are not answering calls from Covid-19 contact-tracers.
Paul Reid says it is a "concerning trend" because they are a valuable resource to protect people against the virus.
This comes after 765 new cases of the virus were confirmed yesterday, but fewer tests were carried in the days around Christmas.
The Irish College Of General Practitioners' Covid Lead, Dr Nuala O'Connor, says GP out of hours services have been very busy throughout the Christmas period.
"There has been a 65 per cent increase in GP referrals for Covid tests in the last week, but I believe that some of the people have not been turning up for the test appointments.
"When people are contacting us, sometimes it's a couple of days that they have had symptoms, so out concern would be what were they doing in those previous few days."
According to the National Public Health Emergency Team (Nphet), Ireland's national 14-day incidence rate has now increased to 220.1.
However, the reduced number of people being tested over Christmas may mean daily case numbers are not a true reflection of the actual level of transmission currently in the country.
In a statement yesterday, Chief Medical Officer Dr Tony Holohan said: "The data we are reporting today are lower than days up to 26 December. This however results from factors related to the time of the year, such as the lower rates of attendance and referrals and presentation for testing for several days over Christmas."
Dr Holohan also said the cumulative number of people hospitalised due to Covid-19 during the current third wave of the virus has already exceeded the number admitted during the second wave.
As of 2pm yesterday, 359 patients were being treated for Covid-19 in hospitals around the country, 30 of whom were in Intensive Care Units.
