The epidemiological characteristics of cluster transmission of coronavirus disease 2019 (COVID-19): a multi-center study in Jiangsu Province

Coronavirus Disease 2019 (COVID-19) pandemic has rapidly spread across the globe while little multi-center research about the epidemiological characteristics of cluster transmission is conducted. To provide a more comprehensive description of the epidemiological characteristics of cluster transmission and the virulence of SARS-CoV-2 carried by asymptomatic carriers, we studied the epidemiological characteristics of 70 clusters. 70 clusters including 311 consecutive subjects from January 20, 2020, to March 10, 2020, were enrolled. Of 70 clusters, 5 were infected by asymptomatic or presymptomatic carriers. We gathered and analyzed information about their demographic, epidemiological, clinical, diagnostic classification, and cluster characteristics. Among the 66 asymptomatic carriers in Jiangsu Province, 49 asymptomatic were observed in 311 subjects distributed in 70 clusters. We demonstrated that there is a significance between the severity of cases infected by asymptomatic carriers and cases infected by symptomatic patients (P=0.033) and the former usually presented with milder symptoms. A significant difference was shown regarding the level distribution of age (P=0.006) and the frequency distribution of gender (P=0.014) and disease severity of COVID-19 (P=0.008) among the seven groups classified by the relationship with the index cases. The average age of infected medical staff was the youngest and the majority of infected medical are females while the infected patients were generally oldest and usually accompanied by severest symptoms. We concluded that asymptomatic carriers are mainly screened out of clusters and the patients infected by asymptomatic carriers present with milder symptoms than those infected by symptomatic patients, which indicated that the SARS-CoV-2 shares decreased virulence among asymptomatic carriers. Effective measures should be taken to prevent transmission in hospitals to protect doctors, nurses, and patients.