LAUSR

ABSTRACT Few studies aimed on the transmission efficiency of asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A follow-up study was performed on 147 asymptomatic carriers in Anhui Province. Of 147 asymptomatic carriers, 50.0% were male, 50.3% cases were older than 40 years, and 43.8% were farmers, 68.7% cases were from north of Anhui Province. There were 16 asymptomatic carriers developed illness in the following 14 days isolated observation, and diagnosed as confirmed cases. The possible latent infection period was evaluated ranged from one to five days before onset, and the median time was two days. The second attack rate of 16 confirmed cases whom transferred from asymptomatic carriers was 9.7% (23/236), while 131 asymptomatic carriers caused 2.6% (24/914) close contacts infection, there was a significant difference of second attack rate among two groups (P＜0.001). Our study indicated that COVID-19 cases are contagious during the incubation period, and the close contact screening should be covered the incubation period. Furthermore, the transmission efficiency of asymptomatic carriers was lower than that of confirmed cases.