Timeline: Pseudomonas outbreak in Londonderry and Belfast

Four babies have died from an outbreak of pseudomonas aeruginosa in Northern Ireland.

One died at a Londonderry hospital, three others in Belfast.

Here is a chronology of events, according to the Regulation and Quality Improvement Authority which has carried out a review.

Altnagelvin Hospital, Londonderry

26 November 2011 - A urine sample from a baby is sent for testing. Two days later this is reported to be positive for pseudomonas aeruginosa.

2 December 2011 - The baby is transferred from Altnagelvin to Belfast for treatment for another condition.

4 December 2011 - Blood cultures are reported to be positive for pseudomonas and this information is passed by phone from Altnagelvin laboratory to the Royal Jubilee Maternity Hospital in Belfast.

6 December 2011 - The condition of a second baby, who had been at the Londonderry hospital from birth, deteriorates. Blood cultures are taken and two days later reported to be positive for the infection.

10 December 2011 - This baby dies. Meanwhile, a third baby at Altnagelvin develops signs of infection and is treated for a presumed diagnosis of pseudomonas infection. Blood tests two days later confirm this.

Neonatal units in Northern Ireland hospitals underwent a deep clean during the outbreak

12 December 2011 - The Western Health and Social Care Trust declares an outbreak at Altnagelvin. Three babies are confirmed as having been infected there. The Public health Agency (PHA) is informed.

14 December 2011 - A Serious Adverse Incident form is submitted to the Health and Social Care Board by the Western Trust.

15 December 2011 - An infected tap and mixer valve are replaced.

19 December 2011 - The Western Trust starts screening babies for both pseudomonas and MRSA.

21 December 2011 - A temporary relocation of the neonatal unit at Altnagelvin takes place to enable a completed disinfection of the water system.

Royal Jubilee Maternity Hospital, Belfast

8 December 2011 - A medical microbiologist informs the Belfast Trust that there are two babies in the Royal Victoria Hospital with pseudomonas.

9 December 2011 - The samples from the two babies are sent to the HPA Reference laboratory in England for typing due to concern that there had been two cases of pseudomonas within one week in the unit.

14 December - A nurse from Altnagelvin advises the Belfast Trust of the outbreak there. The Altnagelvin nurse advises that a sink is the possible source of the infection.

15 December - Preliminary results indicate that the strains of pseudomonas for the two babies at the Royal are different. As there is no evidence for a spread of infection between the babies, the infection in the baby born in the Royal is considered to have been "sporadic".

16 December 2011 The PHA advises Belfast Trust of outbreak at Altnagelvin.

5 January 2012- A baby in the Royal develops respiratory symptoms and a specimen is sent for testing. That baby dies the following day. Two days later it is confirmed that that baby had pseudomonas.

14 January 2012 - Another baby dies at the Royal, having been transferred from Daisy Hill Hospital in Newry. The following day pseudomonas is confirmed in blood cultures.

17 January 2012 - The Belfast Trust declares an outbreak at the Royal Jubilee Maternity Unit.

19 January 2012 - A third baby dies.

Pseudomonas aeruginosa is a relatively common type of infection encountered in UK hospitals

20 January - A press conference is held which involves the Health Minister Edwin Poots, the Belfast Trust and the Public Health Agency. A helpline is established.

30 January 2012 - Health Minister Edwin Poots calls for a review of the circumstances leading to the incidents

4 April2012 - An interim report is published with a final report due by 31 May 2012