GP's are being asked to report any unusual clusters of respiratory illness, following the deaths of six people at a private nursing home in County Donegal.
Visitor restrictions are in place at Nazareth House in Fahan, Buncrana where the deaths took place over the last 12 days.
Laboratory tests and swabs have been taken - and results are due back this evening to determine whether the illness is a viral infection or a strain of flu.
Investigations are being carried out by the HSE and HIQA.
Director of the Health Protection Surveillance Centre, Doctor Darina O'Flanagan says 27 of the remaining residents are showing symptoms, but are not critically ill:
Peter McLoughlin is a member of Buncrana town council.
He says details of the investigation are still emerging: