In December 2019, several cases of “unknown viral pneumonia” were reported in Wuhan City, Hubei Province, China (1). It was named as the 2019 novel coronavirus disease (COVID-19) by the World Health Organization (WHO) (1). In just two months, the virus has spread from Wuhan to other parts of China, and all over the world. By 24:00 on March 8, accumulative 80,735 confirmed cases with 5,111 severe cases, 58,600 cured cases, and 3,119 deaths were documented in China (2). Accumulative 29,215 confirmed cases, 3,343 cured cases and 707 deaths were documented in countries outside of China (3). With the development of the epidemic, the clustered cases were found (4). The incubation period of COVID-19 is generally 3 to 7 days. COVID-19 is also highly contagious in the incubation period (5). The main clinical manifestations are fever, fatigue, dry cough, dyspnea, with or without nasal obstruction, runny nose, and other upper respiratory symptoms. There are also asymptomatic infections (6). Asymptomatic infections make the prevention and control of COVID-19 even harder. This paper reports the discovery process of 4 cases of asymptomatic infected people with familial cluster.
