Asymptomatic carriers of COVID-19 as a concern for disease prevention and control: more testing, more follow-up.

Following a containment phase of two months, China has transitioned to the mitigation phase. However, China still faces the risk of COVID-19 spreading due to not only to sporadic new cases and imported cases but also asymptomatic carriers. According to daily reports from the National Health Commission of the People's Republic of China from March 31, 2020 to April 7, 2020, the number of new asymptomatic cases reported daily greatly exceeded that of new imported cases. As of 24:00 on April 7, there were a total of 1,095 asymptomatic cases with COVID-19 under medical observation on the Chinese mainland, including 358 imported cases. A growing number of studies have indicated that asymptomatic carriers are infectious to an extent and can potentially transmit COVID-19. At present, China's measures for managing asymptomatic carriers are 14 days of centralized quarantine and observation; in principle, people with two consecutive negative nucleic acid tests (at an interval of at least 24 hours) can be released from quarantine. However, asymptomatic carriers will not be included in confirmed cases unless they develop clinical manifestations while in quarantine. As "silent spreaders", asymptomatic carriers warrant attention as part of disease prevention and control. The testing and follow-up of asymptomatic carriers should be expanded to include people in close contact with patients with confirmed COVID-19 and asymptomatic cases, clusters of outbreaks, and key areas and populations with a high risk of infection.