Singleton Hospital's maternity unit is still open for full-term birthsA mother suspected to have contracted an E. coli strain at a maternity unit where two premature babies have died did not pick up the bug at the hospital, say health chiefs.
Her case was initially one of two investigated at Singleton Hospital's maternity and neonatal unit.
Tests now show the mother was carrying a different ESBL E. coli sub-type.
The other case was a premature baby who died after contracting the strain at the unit.
Abertawe Bro Morgannwg (ABM) University Health Board, which runs the hospital, said a second baby who died at the unit had contracted ESBL E. coli elsewhere.
ABM announced on Friday a third baby had tested positive but showed no symptoms.
Tests are under way to see if that baby has the same sub-type as the cross-infection, or whether it is unconnected.
ABM said in a statement: "While these tests are under way, as a continuing precaution, the neonatal unit is restricted to routine admission for babies over 36 weeks' gestation only.
"We are also taking additional precautions, including restricting visitors to the maternity unit and continuing to ask visitors to wash their hands and use hand hygiene gel."
Two other people in the maternity unit were also found to have been infected, but contracted it outside the hospital.
Officials have stressed that ESBL E. coli is not the same as E. coli O157 which causes food poisoning.
They say a very small proportion of people carry ESBL E. coli harmlessly in their body.
ABM added: "Our investigations into the cross infection have not yet identified how the ESBL E. coli was transmitted, but we continue to do all we can to determine the cause.
"However, in other similar instances of this kind elsewhere in the UK the cause of transmission was never identified."
