Epidemiology and Transmission of COVID-19 in Shenzhen China: Analysis of 391 cases and 1,286 of their close contacts

Qifang Bi; Yongsheng Wu; Shujiang Mei; Chenfei Ye; Xuan Zou; Zhen Zhang; Xiaojian Liu; Lan Wei; Shaun A Truelove; Tong Zhang; Wei Gao; Cong Cheng; Xiujuan Tang; Xiaoliang Wu; Yu Wu; Binbin Sun; Suli Huang; Yu Sun; Juncen Zhang; Ting Ma; Justin Lessler; Teijian Feng

Cases detected through symptom-based surveillance were confirmed on average 5.5 days (95% CI 5.0, 5.9) after symptom onset ( Figure 3 , Table S2 ); compared to 3.2 days (95% CI 2.6,3.7) in those detected by contact-based surveillance. 17 cases were isolated before developing symptoms. Among those isolated after, the symptom-based surveillance group were, on average, isolated 4.6 days (95% CI 4.1,5.0) after symptom onset, versus 2.7 days (95% CI 2.1,3.3) in the contact-based surveillance group. Hence, contact-based surveillance was associated with a 2.3 days (95% CI 1.5,3.0) decrease in time to confirmation and a 1.9 days (95% CI 1.1,2.7) decrease in time to isolation. Timings between symptom onset and hospitalization were similar to isolation results ( Figure 3 , Table S2 ).