A continuous age-specific standardized mortality ratio for estimating the unascertained rates in the early epidemic of COVID-19 in different regions

Peipei Du; Peihua Cao; Xiaodong Yan; Daihai He; Xiaotong Zhang; Weixiang Chen; Jiawei Luo; Ziqian Zeng; Yaolong Chen; Lin Yang; Shu Yang; Xixi Feng

doi:10.1080/02664763.2021.1947995

A continuous age-specific standardized mortality ratio for estimating the unascertained rates in the early epidemic of COVID-19 in different regions

J Appl Stat. 2021 Jul 8;50(11-12):2504-2517. doi: 10.1080/02664763.2021.1947995. eCollection 2023.

Authors

Peipei Du^{1

2}, Peihua Cao³, Xiaodong Yan⁴, Daihai He⁵, Xiaotong Zhang², Weixiang Chen², Jiawei Luo⁶, Ziqian Zeng¹, Yaolong Chen⁷, Lin Yang⁸, Shu Yang², Xixi Feng¹

Affiliations

¹ School of Public Health, Chengdu Medical College, Chengdu, People's Republic of China.
² College of Medical Information Engineering, Chengdu University of Traditional Chinese Medicine, Chengdu, People's Republic of China.
³ Clinical Research Center, Zhujiang Hospital, Southern Medical University, Guangzhou, People's Republic of China.
⁴ Zhongtai Securities Institute for Financial Studies, Shandong University, Jinan, People's Republic of China.
⁵ Department of Applied Mathematics, Hong Kong Polytechnic University, Hong Kong, People's Republic of China.
⁶ West China Biomedical Big Data Center, West China Clinical Medical College of Sichuan University, Chengdu, People's Republic of China.
⁷ Evidence-Based Medicine Center, School of Basic Medical Sciences, Lanzhou University, Lanzhou, People's Republic of China.
⁸ School of Nursing, Hong Kong Polytechnic University, Hong Kong, People's Republic of China.

Abstract

The difference in age structure and aging population level was an important factor that caused the difference in COVID-19's case fatality rate (CFR) in various regions. To eliminate the age effect on estimating the CFR of COVID-19, our study applied nonlinear logistic model and maximum likelihood method to fit the age-fatality curves of COVID-19 in different countries and regions. We further computed the standardized mortality ratio from the age-fatality curves of COVID-19 in the above regions and found that the risk of COVID-19 death in Wuhan was of a moderate level, while the non-Hubei region was even lower, compared with other regions. Regarding the disparity of CFRs among different regions in the country, we believed that there might be an unascertained phenomenon in high-endemic regions. Based on age-fatality rate curves, we estimated unascertained rates in cities with severe epidemics such as Wuhan and New York, and it was found that the total unascertained rates in Wuhan and New York were 81.6% and 81.2%, respectively. Meanwhile, we also found that the unascertained rates varied greatly with age.

Keywords: COVID-19; Standardized mortality ratio; age-specific; case fatality rate; nonlinear logistic model.

Grants and funding

The study was funded by the National Natural Science Foundation of China [grant number 81903406], the National Natural Science Foundation of China [grant number 11901352), Natural Science Foundation of Shandong Province [grant number ZR2019BA017], Social Science Foundation of Shandong Province [grant number 35019DTJJ03], the Young Scholars Program of Shandong University [YSPSDU: 11020088964008] and ‘Coronavirus Disease Special Project’ of Chengdu University of Traditional Chinese Medicine [XGZX2013].