At least four times. The control area is divided according to the area covered by the high-frequency activity track of the positive cases or patients in the first 4 days, or the places or areas with certain transmission risks and surrounding areas. Among them, the personnel in the control area should conduct 1 nucleic acid testing within 24 hours. In principle, they should conduct 1 nucleic acid testing every day for the first three days, and then conduct 1 nucleic acid testing every 2-3 days. The number of times can be increased according to actual needs. Therefore, the total number of nucleic acid tests before unsealing the control area should be determined according to the actual situation, but at least four nucleic acid tests should be carried out.