常态化防控下新型冠状病毒肺炎新发疫情研判方法

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

目的介绍研判国内自2020年6月以来新型冠状病毒肺炎(COVID-19)新发疫情在常态化防控背景下首发时间、结束时间及最后规模的首估法和更新法。方法在首个病例确诊后的一个迭代间隔内,首估法运用疫情重心"可能的密切接触(密接)者人数"乘以感染率得到疫情最后规模。在超过半个迭代间隔后,更新法旨在修正疫情的最后规模和结束时间。其中,未来病例数等于现有"处于医学观察者人数"乘以转化率,疫情最后规模为现有病例数与未来病例数之和。首估法和更新法均基于国内前期抗疫积累的经验参数,包括各省、市卫生健康委员会公布的确诊病例数与密接者人数确定的密接到确诊的转化率、具体疫情事件关联的感染率。首发时间的判断则依赖于流行病学调查结果;结束时间则假定为首例病例确诊后的28 d。结果应用首估法和更新法研判北京市、新疆维吾尔自治区乌鲁木齐市和辽宁省大连市的COVID-19新发疫情的首发时间、结束时间和感染者最后规模。根据首例病例确诊3 d内的数据,于2020年6月13日、7月19日和7月24日分别对北京市、乌鲁木齐市和大连市的新发COVID-19疫情,及时给出预判结果并将报告呈送给有关政府部门参考。北京市新发地新发疫情已于2020年7月6日开始清零,累计确诊病例335例,清零时间比本研究预测的7月10日早4 d。结论对疫情的首发时间、结束时间及最后规模的精准研判成为疾控部门疫情早期制定相应措施的一个根本依据。本研究提供了对疫情做及时研判的可行方法。北京市将成为其他省市面对类似新发疫情的一个参考样板。

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 confirmed335 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.