Epidemiological parameters of coronavirus disease 2019: a pooled analysis of publicly reported individual data of 1155 cases from seven countries

Shujuan Ma; Jiayue Zhang; Minyan Zeng; Qingping Yun; Wei Guo; Yixiang Zheng; Shi Zhao; Maggie H Wang; Zuyao Yang

Serial interval was defined as the duration between symptom onset of an infector (e.g., a primary case) and that of an infectee (e.g., a secondary case) in a transmission chain, which was typically seen in cluster infections. A negative value meant that the infectee's symptoms occurred before the infector's symptoms. For two cases to qualify as an infector-infectee pair and be included in this study, the following two criteria must both be fulfilled. First, there was evidence that the presumed infector had been exposed outside the cluster (e.g., close contact with a confirmed case, travel history to Hubei, exposure to a person who returned from Hubei) before he/she joined the group activities such as family gathering and business conference that gave rise to cluster infections. Second, the presumed infectee was exposed to the presumed infector only in the 14 days prior to symptom onset, without other exposure histories.