Estimating the Unreported Number of Novel Coronavirus (2019-nCoV) Cases in China in the First Half of January 2020: A Data-Driven Modelling Analysis of the Early Outbreak
JC School of Public Health and Primary Care, Chinese University of Hong Kong, Hong Kong 999077, China
Shenzhen Research Institute of Chinese University of Hong Kong, Shenzhen 518060, China
Department of Applied Mathematics, Hong Kong Polytechnic University, Hong Kong 999077, China
Michigan Institute for Data Science, University of Michigan, Ann Arbor, Michigan, MI 48104, USA
School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong 999077, China
Department of Orthopaedics and Traumatology, Chinese University of Hong Kong, Hong Kong 999077, China
SH Ho Scoliosis Research Lab, Joint Scoliosis Research Center of Chinese University of Hong Kong and Nanjing University, Hong Kong 999077, China
School of Mathematics and Statistics, Huaiyin Normal University, Huaian 223300, China
School of Nursing, Hong Kong Polytechnic University, Hong Kong 999077, China
Department of Mathematics, Shanghai Normal University, Shanghai 200234, China
Authors to whom correspondence should be addressed.
J. Clin. Med. 2020, 9(2), 388; https://doi.org/10.3390/jcm9020388
Received: 27 January 2020 / Revised: 29 January 2020 / Accepted: 31 January 2020 / Published: 1 February 2020
(This article belongs to the Special Issue Real Time Clinical and Epidemiological Investigations on Novel Coronavirus - Part I)
Background: In December 2019, an outbreak of respiratory illness caused by a novel coronavirus (2019-nCoV) emerged in Wuhan, China and has swiftly spread to other parts of China and a number of foreign countries. The 2019-nCoV cases might have been under-reported roughly from 1 to 15 January 2020, and thus we estimated the number of unreported cases and the basic reproduction number, R0, of 2019-nCoV. Methods: We modelled the epidemic curve of 2019-nCoV cases, in mainland China from 1 December 2019 to 24 January 2020 through the exponential growth. The number of unreported cases was determined by the maximum likelihood estimation. We used the serial intervals (SI) of infection caused by two other well-known coronaviruses (CoV), Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) CoVs, as approximations of the unknown SI for 2019-nCoV to estimate R0. Results: We confirmed that the initial growth phase followed an exponential growth pattern. The under-reporting was likely to have resulted in 469 (95% CI: 403–540) unreported cases from 1 to 15 January 2020. The reporting rate after 17 January 2020 was likely to have increased 21-fold (95% CI: 18–25) in comparison to the situation from 1 to 17 January 2020 on average. We estimated the R0 of 2019-nCoV at 2.56 (95% CI: 2.49–2.63). Conclusion: The under-reporting was likely to have occurred during the first half of January 2020 and should be considered in future investigation.