Using a retrospective cross-sectional study to analyse unintentional fatal drowning in Australia: ICD-10 coding-based methodologies verses actual deaths

OBJECTIVES: Fatal drowning estimates using a single underlying cause of death (UCoD) may under-represent the number of drowning deaths. This study explores how data vary by International Classification of Diseases (ICD)-10 coding combinations and the use of multiple underlying causes of death using a national register of drowning deaths. DESIGN: An analysis of ICD-10 external cause codes of unintentional drowning deaths for the period 2007–2011 as extracted from an Australian total population unintentional drowning database developed by Royal Life Saving Society—Australia (the Database). The study analysed results against three reporting methodologies: primary drowning codes (W65-74), drowning-related codes, plus cases where drowning was identified but not the UCoD. SETTING: Australia, 2007–2011. PARTICIPANTS: Unintentional fatal drowning cases. RESULTS: The Database recorded 1428 drowning deaths. 866 (60.6%) had an UCoD of W65-74 (accidental drowning), 249 (17.2%) cases had an UCoD of either T75.1 (0.2%), V90 (5.5%), V92 (3.5%), X38 (2.4%) or Y21 (5.9%) and 53 (3.7%) lacked ICD coding. Children (aged 0–17 years) were closely aligned (73.9%); however, watercraft (29.2%) and non-aquatic transport (13.0%) were not. When the UCoD and all subsequent causes are used, 67.2% of cases include W65-74 codes. 91.6% of all cases had a drowning code (T75.1, V90, V92, W65-74, X38 and Y21) at any level. CONCLUSION: Defining drowning with the codes W65-74 and using only the UCoD captures 61% of all drowning deaths in Australia. This is unevenly distributed with adults, watercraft and non-aquatic transport-related drowning deaths under-represented. Using a wider inclusion of ICD codes, which are drowning-related and multiple causes of death minimises this under-representation. A narrow approach to counting drowning deaths will negatively impact the design of policy, advocacy and programme planning for prevention.