Changing case fatality risk for COVID-19 over time in selected European countries (preprint)

Objectives To illustrate the development of the case fatality risk (CFR) for COVID-19 over time using different assumptions for calculating the CFR. Design Observational study. Setting Selected European countries, 28 January to October 29 2020. Participants Laboratory-confirmed COVID-19 cases and deaths due to COVID-19 Main outcome measure case fatality risk (CFR) Results We show that the CFR has considerably decreased over time. This seems to be driven not only by increased testing but also by a reduced CFR among cases older than 60 years. Our data also confirm a significantly higher fatality risk for men than for women. The decline in the CFR is even more pronounced when only cases and deaths occurring in a specified time window are considered. This alternative estimation method has the advantage that early data where the bias due to the incomplete ascertainment of cases was arguably largest do not affect CFR estimates later on. We find similar results for other European countries. Conclusion CFR estimates vary considerably depending on the underlying assumptions concerning their calculation. Reliable CFR estimates should not be based on cumulative numbers from the beginning of the pandemic but rather be based on more recent data only.

The Role of Age Distribution, Time Lag Between Reporting and Death and Healthcare System Capacity in Case Fatality Estimates of COVID-19 (preprint)

Background: European countries report large differences in coronavirus disease (COVID-19) case fatality risk (CFR). CFR estimates depend on demographic characteristics of the cases, time lags between reporting of infections and deaths and infrastructural characteristics, such as healthcare and surveillance capacities. Methods: We used publicly available data from official reports of the national health authorities of Germany, Italy, France, and Spain on COVID-19. These include age-specific numbers of cases and deaths for different dates, which we used to compute age-standardized CFR ratios using a standard European population for standardization. Moreover, we investigated the impact of different potential time lags on the estimation of the CFR using data published by the European Centre for Disease Prevention and Control (ECDC). Finally, we described the association between case fatality and the intensive care bed capacity.Results: We found that age-standardized CFR estimates increased from the beginning of March to mid-May 2020 in all included European countries. In Germany, CFRs are lower than in other countries. However, the differences are much larger when comparing the crude risks rather than the age-adjusted risks. Thus, the different age distribution of the cases account for a major proportion of the reported differences. Case fatality estimates using time lags of 1-10 days converged in all countries over time, however, there is no optimal time lag to assess the CFR during the pandemic. Time lags that provided the most constant estimates and approach best the observed CFR after the pandemic ranged from 5-10 days in different countries and at different time points during the pandemic. For the association between intensive care bed capacity and fatality we found that days with a high need for intensive care beds were positively correlated with daily hospitalization fatality in France, Italy, and Spain, but not in Germany.  Conclusions: Our results highlight that cross-country comparisons of crude CFR estimates can be misleading and should be avoided. However, to adjust for potential sources of bias more disaggregated data and information on surveillance and health care capacities are needed. Filling these gaps and harmonizing data across European countries will facilitate further analysis. 

The role of age distribution, time lag between reporting and death and healthcare system capacity on case fatality estimates of COVID-19 (preprint)

European countries report large differences in coronavirus disease (COVID-19) case fatality risk (CFR). CFR estimates depend on demographic characteristics of the cases, time lags between reporting of infections and deaths and infrastructural characteristics, such as healthcare and surveillance capacities. We discuss the impact of these factors on the CFR estimates for Germany, Italy, France, and Spain for the COVID-19 pandemic from early March to mid-April, 2020. We found that, first, a large proportion of the difference in CFRs can be attributed to different age structures of the cases. Second, lags of 5-10 days between day of case report and death should be used, since these provide the most constant estimates. Third, for France, Italy, and Spain, intensive care beds occupied by COVID-19 patients were positively associated with fatality risks of hospitalized cases. Our results highlight that cross-country comparisons of crude CFR estimates can be misleading and should be avoided.