Assessment method of coronavirus disease 2019 outbreaks under normal prevention and control

  Objective  We introduce methods for assessing the first outbreak time, the final size and the stop time for the coronavirus disease 2019 (COVID-19) outbreaks in China since June 2020.

  Methods  Within one serial interval after the confirmation of the first case, Theoretical Principal Estimation should be performed by taking the product of the number of probable close contacts around the epidemic barycenter and the infection rate. When days exceed half serial interval, the aim of Theoretical Update Estimation is to improve the estimation of the final size and stop time. The number of future probable cases is equal to the product of the current number of isolated close contacts with the conversion rate of isolation to confirmation. The final size is the sum of numbers of current confirmed cases and future probable cases. Both estimation methods are based on the experiences of domestic anti-epidemic in the early stage, including conversion rates of isolated close contacts to confirmed case by the data from 30 Health Commissions of China, and infection rate calculated by the data from four events. The date of the first infected case usually depends on the epidemiological investigations. Together with the current normalization prevention and control in China, it is reasonable to assume that a COVID-19 outbreak should end within 28 days after the first case was diagnosed.

  Results  The COVID-19 outbreaks that occurred mainly in Beijing, Urumqi and Dalian since June 2020 were studied by the proposed Theoretical Principal Estimation and Theoretical Update Estimation to predict the date of the first infected case, the stop time of the epidemics and the final size. According to the data within three days of the confirmation of the first case, the principal results around the date of the first infected case, the stop time and final size of the epidemic were respectively sent to Beijing, Urumqi and Dalian governmental sides as references on June 13, July 19 and July 24 of 2020. Since July 6 of 2020, the COVID-19 outbreak in Beijing began to clear with the total number of confirmed 335 cases, which was less 4 days than the theoretical prediction in this paper.

  Conclusion  The precise estimation of the three important indicators, namely the date of the first infected case, the stop time and final size of the epidemic, is fundamental for the disease control agencies to formulate corresponding measures. The present study provides methods for making quick and usual prediction. The rapid control by Beijing city's disease control agency will be a reference model for similar epidemics in the future.