There might have been a delay in putting pseudomonas control measures in place because health trusts had different approaches to declaring outbreaks, a review into the outbreak has said.
It criticised a lack of communication between health officials.
Three babies died in the Royal Jubilee Maternity Unit in January, while another newborn died at Londonderry's Altnagelvin Hospital the previous month.
Review chairwoman Professor Pat Troop told Stormont's health committee: "It is normal for one case not to trigger an outbreak. From now on one case should trigger a series of actions that have not been standardised before."
During the alert, chief medical officer Dr Michael McBride sent a circular to all trusts.
Professor Troop added: "We have had some information on what they did but not enough. I cannot really say how much difference it would have made until we have gotten down to the detail."
The review team found that staff in all trusts acted to reduce risks of spread of infection and to investigate why the incidents had occurred.
Information about cases which had occurred in other trusts was not always readily available to inform critical decisions, the report said.
"There is no agreed system for the surveillance of pseudomonas colonisation and infection and this led to delays in sharing of information between trusts. It is recommended that a surveillance system is established as soon as possible.
"Trusts had different approaches to the declaration of outbreaks. This may have led to a delay in putting control measures in place when cases of infection occurred. It is recommended that an agreed approach is established across all trusts."