There has been a confirmed case of the H1N1 flu virus at Cork University Hospital.
Commonly known as swine flu, the hospital said some other patients are displaying symptoms of the virus but are not confirmed as suffering from it.
As a precaution, the hospital has closed off one ward and introduced visitor restrictions.
A consultant microbiologist at the hospital has said the regular flu vaccine will be enough to protect people against the swine flu virus.
Speaking on RTÉ's Morning Ireland, Dr Bartley Cryan said visiting restrictions had been introduced after an increase in the number of flu cases at the hospital.
Latest statistics from the Health Protection Surveillance Centre show that the flu outbreak is above the national threshold, with cases on the rise across the country.
The figures show that 34 confirmed hospitalised influenza cases were reported to the centre in the past week, bringing the total number to 118.
The flu outbreak is above the national threshold of 21 cases per 100,000 and now stands at 42.5 per 100,000.
The centre expects this to drop back in the coming weeks.
Dr Darina O'Flanagan, from the Health Protection Surveillance Centre, said this is not a pandemic and flu levels are nowhere near where they were during the pandemic of 2009/2010.