The size of the infection rate of close contacts of the new crown is mainly related to the length of time of exposure to the virus, their own immunity, protective measures, etc., and the close-contact population needs to be centralized isolation and observation as well as home isolation, and nucleic acid testing of the new crown needs to be done during the isolation period. 1. The length of virus contact time: the longer the contact time between the close contacts and the new coronavirus infected people, the greater the possibility of infection. 2. Autoimmunity: Contacts with strong autoimmunity are relatively less likely to be infected, so elderly patients or those with underlying diseases tend to be the high prevalence group. 3. Protective measures: close contacts wear masks when contacting patients, and clean their hands in a timely and effective manner after contact, which is relatively less likely to be infected. For close contacts of the chance of infection can not be determined, so for close contacts should also be isolated for observation. Close contacts are generally subject to intensive isolation and observation, and are required to undergo two consecutive negative nucleic acid tests before being released from isolation, and are required to be isolated at home after isolation and observation has been completed. Specific quarantine and nucleic acid testing policies are based on local conditions.