Common Comorbidities and Complications in COVID-19 Deaths: An Analysis from Italian Data in Comparison with Influenza

Multiple cause data refer to all conditions reported on death certificates. Compared to the single underlying cause of death, these data provide additional information concerning the presence of comorbidities and complications leading to death. The objective of the study is to use a novel multiple cause approach for identifying comorbidities and complications of COVID-19. We analysed certificates referring to deaths that occurred in Italy in 2020–2021. With a double step chi squared test, we identified the conditions associated with COVID-19 and whether such conditions were reported as ‘cause of’ (comorbidities) or ‘due to’ (complications) COVID-19. For comparison, we adopted the same procedure for influenza deaths that occurred in Italy in 2016–2019. Pneumonia, respiratory failure and adult respiratory distress syndrome are the most frequent complications of COVID-19 and are also associated with it. These diseases have the same role for influenza, nevertheless this latter is strongly associated also with heart failure reported as a complication. Comorbidities are similar for COVID-19 and influenza: diabetes mellitus, chronic obstructive pulmonary disease (COPD) and obesity are the most frequent, with obesity much more frequent in COVID-19 cases. Hypertension is strongly associated with COVID-19 and is more frequent than in influenza cases. This approach is also suitable for other target diseases.