key: cord-287209-hkrarxsd
authors: Zhao, Shi; Lin, Qianyin; Ran, Jinjun; Musa, Salihu S; Yang, Guangpu; Wang, Weiming; Lou, Yijun; Gao, Daozhou; Yang, Lin; He, Daihai; Wang, Maggie H
title: The basic reproduction number of novel coronavirus (2019-nCoV) estimation based on exponential growth in the early outbreak in China from 2019 to 2020: A reply to Dhungana
date: 2020-02-20
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.02.025
sha: 
doc_id: 287209
cord_uid: hkrarxsd

nan

To the editor The ongoing outbreak of the novel coronavirus (2019-nCoV) pneumonia in Wuhan, China and other regions remains a major public health concern. We thank Dhungana's comments to our study, Zhao et al. [1] , recently published in the International Journal of Infectious Diseases. The estimates on the basic reproduction number, R0, were carried out in early outbreak as of January 22, 2020 when the surveillance data and the knowledge on the key epidemiological features of 2019-nCoV were limited.

The assumptions of exponential growth as well as other similar growing patterns are commonly accepted and adopted to capture the growing trends during the early phase of an outbreak [2] [3] [4] . The exponential growing rate (γ), or the intrinsic growing rate, is estimated from the early epidemic curve and used to calculate the R0.

We repeat the analysis in Zhao et al. [1] , γ is estimated at 0.18 (95%CI: 0.14−0.22), 0.15 (95%CI: 0.12−0.18) and 0.11 (95%CI: 0.09−0.13) per day associated with 2-, 4-and 8-fold increase in the reporting rate, respectively. By using the serial interval (SI) estimate (mean ± SD at 7.5 ± 3.4 days) from Li et al. [5] , we found the R0 at 3.33 (95%CI: 2.17−4.04), 2.69 (95%CI: 2.28−3.17) and 2.13 (95%CI: 1.88−2.42) associated with 2-, 4-and 8-fold increase in the reporting respectively. Our estimates were in line with the WHO estimates in both early version (2-fold case) and the published version. The key message as we highlighted in the paper is the changes in reporting rate. This is recently reconfirmed by Tuite and Fishman [6] . We thank the editor and Dhungana to give us this opportunity to reclarify our key message that the reporting rate was not constant during the early outbreak and could affect the estimation of R0. There is indeed a large amount of later confirmed cases which were not counted in the early official daily situation reports [5, [7] [8] [9] . In other words, if the same reporting standard in the second half of January was applied to the first half of January, the number of cases would be much higher. Other teams either used retrospective dataset which was not publicly available on January 23, 2020 or used oversea reported cases which was not (to a much less extent) affected by the changes in reporting rate. By using the same analysis and dataset as in Zhao et al. [1] , an additional sensitivity analysis on the R0 estimates and varying SI and reporting rate was conducted and shown in Fig 1. We report that R0 estimates increase while the mean of SI increases or the SD of SI decreases. By selecting mean between 7 and 8 days and SD between 3 and 4 days for SI of 2019-nCoV, the R0 estimates are largely consistent within a range from 2 to 4 in many existing literatures [5, [7] [8] [9] [10] , see panels (f), (g), (j) and (k) Fig 1. We conclude that our previous estimation and main conclusions in [1] hold based on the reasonable selection of the SI estimates of 2019-nCoV. Not only our early version (2-fold case) is in line with the WHO estimates, but also we pointed out the issue in the reporting rate changes in the official reported cases. The estimates of the basic reproduction number, R0, with varying reporting rates, mean and SD of serial interval (SI). The mean of SI, from top to bottom vertically, varies at 6, 7, 8 and 9 days. The SD of SI, from left to right horizontally, varies at 2, 3, 4 and 5 days. The light-yellow area highlights the R0 ranging from 2 to 4 referring to the estimates in [5, [7] [8] [9] [10] . The blue bold curve is the mean estimate, and the blue dashed curves are the 95% confidence interval (95%CI).

Preliminary estimation of the basic reproduction number of novel coronavirus (2019-nCoV) in China, from 2019 to 2020: A data-driven analysis in the early phase of the outbreak

Early transmission dynamics of Ebola virus disease (EVD)

The basic reproductive number of Ebola and the effects of public health measures: the cases of Congo and Uganda

Appropriate models for the management of infectious diseases

Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus-Infected Pneumonia

Reporting, Epidemic Growth, and Reproduction Numbers for the 2019

Novel Coronavirus (2019-nCoV) Epidemic. Annals of Internal Medicine

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The authors thank Cindy Y Tian from the Chinese University of Hong Kong for helping on processing the reference files.J o u r n a l P r e -p r o o f

The authors declared no competing interests.

All authors conceived the study, carried out the analysis, discussed the results, drafted the first manuscript, critically read and revised the manuscript, and gave final approval for publication.