Traces of a deadly infection which killed four babies in hospitals in Northern Ireland have been found in three more neonatal units.

Health officials said the pseudomonas bacteria has been detected in water outlets at Daisy Hill Hospital in Newry, Co Down, Craigavon Area Hospital in Co Armagh and the Erne Hospital in Co Fermanagh. The Public Health Agency said no babies in these three hospitals had been infected.

Separate outbreaks claimed the lives of one newborn at Altnagelvin Hospital in Londonderry in December and three at the Royal Jubilee Maternity Hospital in Belfast last month.

Traces of the infection were also detected in the neonatal unit at the Ulster Hospital on the outskirts of Belfast last month, though no infants contracted it.

While no infants were infected at Daisy Hill, Craigavon and the Erne, two babies in the Craigavon unit did have traces of the bacteria on their skin. In all six hospitals where the bacteria has been detected, the water systems were the source.

A spokeswoman from the PHA said measures were already in place at neonatal units throughout Northern Ireland to ensure that babies do not come in contact with pseudomonas, with only sterile water used in the direct care of newborns.

Taps in all neonatal facilities in the region are currently being replaced as a result of the outbreaks, with tests being carried out on water samples in all these units.

The PHA spokeswoman added: "It is not clear at this stage exactly what the implications are of finding pseudomonas in water supplies and what longer-term monitoring is required.

"National guidance is being developed urgently for the whole of the UK, with experts taking account of all of the scientific evidence available, including the evolving situation in Northern Ireland."

Stormont Health Minister Edwin Poots has claimed that health trusts may not have acted quickly enough to prevent hospital outbreaks of the deadly infection. Announcing an independent investigation into the pseudomonas bacteria emergencies in three neonatal units, Mr Poots told the Assembly last month that the actions of trust officials needed to be rigorously examined.