The NEW ENGLAND JOURNAL f MEDICINE ORIGINAL ARTICLE Early Transmission Dynamics in Wuhan,China, of Novel Coronavirus-Infected Pneumonia Kathy S.M.Leung.Ph.D..Eric H.Y.Lau,Ph.D.Jessica Y.Wong.Ph.D. Xuesen Ph.Njuan M.Med.Yang Wu Mc.P.H. Man i en. Rui Yang.M.Med.Oi Wang.M.P.H.Suhua Zhou.M.Med.Rui Wane.M.D. Hui Liu,M.Med.,Yinbo Luo,M.Sc..Yuan Liu,M.Med.,Ge Shao,B.Med., Huan Li,M.P.H.Zhongfa Tao,M.P.H.,YangYang,M.Med. M.Me L n Bo Yang,M.Sc..Gabriel M.Leung,M.D.and Zijian Feng,M.Med. ABSTRACT BACKGROUND The initial c eof novel coronus 1Cov)infted pneumoni (N) er2019 and eng at the d Pr ing District.Bi ing.C on on de ic characteri sure history, Gogt d by of January 22,2020.We described characteristics of the cases and estimated the kev time-deyinthe priod ofonhwe at the Hubei Ce y:or to D estimated the epidemic doubling time and the basic reproductive number. Control a Prevention,Ne the first 425 atithid NCIP thedia Hubei.China.or. and 56 er The majority of cases (55%)with onset before an were linked to the Huanan Seafo Wholesale Market,as compared with 959 artide tages the epidemic doubled in size every 4 ays.With a mean serial interal of 7.5 days%Cl,5.3 to1),the basic reproductive number was estimated to be 20 2.295%C1.1.4to3.9). eais of this normtion there is evidence that has occurred among close contacts since the middle of December 2019.Considerable efforts to reduce transmission will be required to control outbreaks if similar dy amics apply el nistry o N ENGLI MED NEIMOROThe new england journal o f medicine n engl j med nejm.org 1 The authors’ affiliations are listed in the Appendix. Address reprint requests to Dr. Feng at the Chinese Center for Dis￾ease Control and Prevention, No. 155 Changbai Rd., Changping District, Bei￾jing, China, or at fengzj@chinacdc.cn; to Dr. G.M. Leung or Dr. Cowling at the School of Public Health, Li Ka Shing Fac￾ulty of Medicine, University of Hong Kong, 21 Sassoon Rd., Pokfulam, Hong Kong, China, or at gmleung@hku.hk or bcowling@hku.hk, respectively; or to Dr. B. Yang at the Hubei Center for Disease Control and Prevention, No. 35 Zhuodao￾quan North Rd., Hongshan District, Wuhan, Hubei, China, or at 49205957@qq.com. Drs. Q. Li, X. Guan, P. Wu, and X. Wang and Drs. B. Cowling, B. Yang, M. Leung, and Z. Feng contributed equally to this article. This article was published on January 29, 2020, and last updated on January 31, 2020, at NEJM.org. DOI: 10.1056/NEJMoa2001316 Copyright © 2020 Massachusetts Medical Society. BACKGROUND The initial cases of novel coronavirus (2019-nCoV)–infected pneumonia (NCIP) oc￾curred in Wuhan, Hubei Province, China, in December 2019 and January 2020. We analyzed data on the first 425 confirmed cases in Wuhan to determine the epidemio￾logic characteristics of NCIP. METHODS We collected information on demographic characteristics, exposure history, and illness timelines of laboratory-confirmed cases of NCIP that had been reported by January 22, 2020. We described characteristics of the cases and estimated the key epidemiologic time-delay distributions. In the early period of exponential growth, we estimated the epidemic doubling time and the basic reproductive number. RESULTS Among the first 425 patients with confirmed NCIP, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period was 5.2 days (95% confidence inter￾val [CI], 4.1 to 7.0), with the 95th percentile of the distribution at 12.5 days. In its early stages, the epidemic doubled in size every 7.4 days. With a mean serial interval of 7.5 days (95% CI, 5.3 to 19), the basic reproductive number was estimated to be 2.2 (95% CI, 1.4 to 3.9). CONCLUSIONS On the basis of this information, there is evidence that human-to-human transmission has occurred among close contacts since the middle of December 2019. Considerable efforts to reduce transmission will be required to control outbreaks if similar dy￾namics apply elsewhere. Measures to prevent or reduce transmission should be imple￾mented in populations at risk. (Funded by the Ministry of Science and Technology of China and others.) ABSTRACT Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus–Infected Pneumonia Qun Li, M.Med., Xuhua Guan, Ph.D., Peng Wu, Ph.D., Xiaoye Wang, M.P.H., Lei Zhou, M.Med., Yeqing Tong, Ph.D., Ruiqi Ren, M.Med., Kathy S.M. Leung, Ph.D., Eric H.Y. Lau, Ph.D., Jessica Y. Wong, Ph.D., Xuesen Xing, Ph.D., Nijuan Xiang, M.Med., Yang Wu, M.Sc., Chao Li, M.P.H., Qi Chen, M.Sc., Dan Li, M.P.H., Tian Liu, B.Med., Jing Zhao, M.Sc., Man Liu, M.Sc., Wenxiao Tu, M.Med., Chuding Chen, M.Sc., Lianmei Jin, M.Med., Rui Yang, M.Med., Qi Wang, M.P.H., Suhua Zhou, M.Med., Rui Wang, M.D., Hui Liu, M.Med., Yinbo Luo, M.Sc., Yuan Liu, M.Med., Ge Shao, B.Med., Huan Li, M.P.H., Zhongfa Tao, M.P.H., Yang Yang, M.Med., Zhiqiang Deng, M.Med., Boxi Liu, M.P.H., Zhitao Ma, M.Med., Yanping Zhang, M.Med., Guoqing Shi, M.P.H., Tommy T.Y. Lam, Ph.D., Joseph T. Wu, Ph.D., George F. Gao, D.Phil., Benjamin J. Cowling, Ph.D., Bo Yang, M.Sc., Gabriel M. Leung, M.D., and Zijian Feng, M.Med. Original Article The New England Journal of Medicine Downloaded from nejm.org at SOUTHERN MEDICAL UNIVERSITY on March 6, 2020. For personal use only. No other uses without permission. Copyright © 2020 Massachusetts Medical Society. All rights reserved