According to WHO's rules, any death certificate must state the underlying cause of death and contributory causes of death may also be stated.

Differentiating between primary and secondary drowning is difficult, as information preceding the drowning incident is rarely available. Yet, knowing the most frequent causes of secondary drowning may provide useful information to healthcare professionals working in prehospital Emergency Medical Services, as this may affect prehospital treatment.

The annual death statistics are based solely on the underlying cause of death, that is the disease or condition which started the process that led to death. The conditions that directly caused the death are also to be stated by the physician on the death certificate and may be included in the statistics. In research projects, data on those contributory causes of death may be drawn from the register. It is now the medical doctor who has verified the death and issued the death certificate indicating the underlying and contributory causes of death, who also classifies these causes in accordance with ICD-10 and fills in the coded data on the electronic death certificate. The Danish Register of Causes of Death is, thus, updated without central validation of the classification and relies entirely on the coding done by individual physicians.

This study aims to characterise fatal drowning incidents as primary or secondary drownings and report the frequencies of secondary drowning causes.

Inclusion Criteria:

• All drowning patients registered in the Danish Prehospital Drowning Data AND
• Having a fatal outcome within 30 days after the drowning incident AND
• Having a valid civil registration number in the Danish Prehospital Drowning Data
• Being able to link data from the Danish Register of Causes of Death

Exclusion Criteria:

• Patients alive 30 days after the drowning incident
• Patients with an invalid civil registration number in the Danish Prehospital Drowning Data
• Patients where data cannot be retrieved from the Danish Register of Causes of Death

The Danish Prehospital Drowning Data reports prehospital data on patients with fatal and non-fatal drowning treated by the Emergency Medical Services in Denmark since 2016. Drowning incidents are identified from the Danish Prehospital Electronic Medical Record using the Danish Drowning Formula and extensive manual validation. Data is extracted following the revised USFD. The patients' unique civil registration number enable linkage with the Civil Personal Register to obtain data on 30-day survival and differentiate between fatal and non-fatal drowning incidents

The data are available upon reasonable request from researchers after application to the corresponding author, provided the necessary approvals are obtained from the relevant authorities.