A new method for accurate calculation of case fatality rate during a pandemic (Preprint)

BACKGROUND In course of an epidemic of a potentially fatal disease, it is difficult to well estimate the case fatality rate (CFR). OBJECTIVE Taking the coronavirus disease-2019 (COVID-19) as an example, this study aims to develop a new method for CFR calculation while a pandemic is ongoing. METHODS We developed a new method for CFR calculation, which was based on the formula: the number of deaths divided by the number of cases T days before, where T is an average delay between case confirmation and disease outcome. In this study, T was screened from a series of hypothesized values. Objective law was found from simulated data that if a hypothesized T was equal to the true T, calculated real-time CFRs kept constant; If a hypothesized T was greater (or smaller) than the true T, real-time CFRs would infinitely decrease (or increase) to near the true CFR with the days went on. RESULTS Based on the discovered law, it was estimated that the true CFR of COVID-19 at the initial stage of pandemic in China except Hubei Province was 0.8%; Hubei Province was 6.6%. The calculated CFRs had predicted the death numbers with almost complete accuracy. CONCLUSIONS The method could be used for accurate calculation of the true CFR during a pandemic instead of waiting till the end, no matter the pandemic was under control or not. It could help outbreak-controller indirectly to have a clear vision in the timeliness of the case confirmation.