A cluster of the Corona Virus Disease 2019 caused by incubation period transmission in Wuxi, China

•The cluster's source was the first-generation, who contacted with Wuhan people during the annual meeting from January 15 to 16.•This cluster involved four generations of cases, each of which was transmitted to the next generation during the incubation period.•It was contagious 9 days before the onset of illness.•Two patients in this cluster were tested positive for the nucleic acid of the COVID-19 virus again during isolation and observation after discharge. The infectivity and transmission capacity of COVID-2019 cases during the incubation period are not very clear. The manuscript described a cluster to provide information for research on incubation period infection. We collected the required data from “Public Health Emergency Reporting Management Information System”, epidemiological questionnaires for the cases, and laboratories. The cluster involved four generations, each of which was transmitted to the next generation during the incubation period. The time was 2–7 days, 6–7days, 3–8 days and 9 days prior to onset. As of March 11, the fourth-generation cases had no symptoms. Combined with the epidemiological data, we inferred that the source of the cluster was caused by the first-generation, who contacted with more than ten Wuhan people during the annual meeting from January 15 to 16. Two cases in this cluster were tested positive again during isolation and observation after discharge. We determined incubation period was infectious, and confirmed that it was contagious 9 days before the onset. The patients who were discharged might need to be observed for a period of time. This study was useful for the practical work, such as in the investigation of close contacts.