COVID-19 as cause of death: a bridge coding study.

Background: The number of COVID-19 deaths is an important measure for the impact of the pandemic. However, estimates differ and fuel the debate on COVID-19 as legitimate cause of death. Objective: To study the role of COVID-19 as cause of death. Methods: Double (bridge) coding of all death certificates mentioning COVID-19 in the Dutch cause-of-death registry during the pandemic 2020-2022 (n=51,288). The coding of records by the WHO special instruction for COVID-19 as issued in April 2020 was compared with the coding of the same set of records by the prevailing rules of the ICD-10 and the effect on cause-of-death statistics was studied. Results: When mentioned on a death certificate, COVID-19 was selected as underlying cause of death in 94% of the cases by the WHO special instruction. According to the prevailing ICD-10 coding rules, COVID-19 was the beginning of a causal sequence leading to death in 76% of the cases (General Principle) and when the role of contributing co-morbidity was taken in to account too (Direct Sequel), COVID-19 was the underlying cause of death in 49% of the cases. These different estimates can be explained by a difference in perspective. The WHO special instruction identifies cases from an epidemiological point of view (surveillance), while the prevailing ICD-10 rules identify cases with COVID-19 as a necessary Conclusion: Different estimates of COVID-19 deaths represent different views on the role of COVID-19 as cause of death, which should be taken in to account when interpreting cause-of-death statistics.