Published Thursday, 02 July 2009
It is understood one of the cases is a sibling of one of three pupils at St Ronan's Primary School in Newry who have contracted the virus.
According to the Health Minister Michael McGimpsey all four are recovering well.
Experts predict a steep rise in cases over the summer, perhaps as many as 100,000 a day across the UK.
National Health Secretary Andy Burnham said that the UK has now moved past the stage of containing the outbreak and into the "treatment phase".
"We have reached the next step in our management of the disease," he told the House of Commons.
Thirty-eight cases are now being treated in Northern Ireland, and the number of patients treated in Ireland has passed the 50 mark.
On Wednesday the province's Health Minister Michael McGimpsey predicted that a third of the population, some 600,000 people, are likely to get swine flu in the months ahead.
Mr McGimpsey also announced that the routine testing of people with suspected swine flu is now being scrapped together with the tracing of close contacts of those with symptoms.
Antivirals will also no longer be used as a preventative measure against swine flu, he added.
The change of policy was confirmed following a meeting of the UK's Health Ministers at the Government Cobra Committee in London on Wednesday.