This is a multicentre observational study involving NNUs across the UK. Study personnel (Neonatologists and research Nurses) from these NNUs will identify eligible babies in whom a positive culture has been obtained.

This study will help identify the infections leading to death in babies on UK neonatal units, define the clinical characteristics of babies dying from infections, and describe the management of babies dying from infections with a specific focus in their antimicrobial treatment.

The neonIN surveillance network captures data on episodes of invasive neonatal infection on a web-based database. Over 30 UK neonatal units currently contribute to this database in real-time. An episode of neonatal infection is defined as a positive culture collected from a normally sterile site such as the blood, cerebrospinal fluid (CSF) or urine (via catheter or suprapubic aspirate) for which clinicians prescribed at least five days of appropriate antibiotics. Clinical, demographic and microbiological data (including antimicrobial susceptibilities) are collected using a standardised online questionnaire. Denominator data regarding the total number of live-births and neonatal-admissions are collected for each neonatal unit.

Through our study we aim to understand and describe better those infections and risk factors that lead to death. The case-control study will enable us to determine if gaps in optimal management, such as the wrong antibiotic or the wrong dose, are associated with poor outcomes. We can then translate such information into practice and develop / improve clinical guidance in order to improve outcomes.

For the purpose of this study, we will request information on the baby's status (alive/died/not known) at 28 days after the positive culture was obtained. If the baby is alive, then this baby becomes eligible as a control. If the baby has died, then further details will be sought including the date of death and whether death was attributed to the infection.

Inclusion criteria:

• Infants on participating NNUs who have an episode of infection with a positive culture.

Neonatal units

All collected individual participant data will be made available to all researchers.

Clinical Study Report will be made available in the form of a publication within 6 months of study end date.

Only team members who have access to the database will be able to view study data for their individual site. Sites can also view reports of the general study on the database. The lead site will have capacity to review the full study data for statistical analysis.