If the infected person is in the incubation period, the nucleic acid test may also be negative, at this time can not be completely excluded from the infectious. If the infected person in the incubation period, at this time can not have any clinical symptoms, and the viral load is low, nucleic acid test can not be positive, but after 1~7 days, the virus replication increased, again nucleic acid test may be positive, become asymptomatic infected or diagnosed cases. So the virus is also present in the body during the incubation period, just in smaller quantities, and it is also contagious. Therefore, a negative nucleic acid test should not be taken lightly, and two or more tests should be conducted. If the nucleic acid test result is still negative, it can be considered that the patient is not infected; if the nucleic acid test result is positive, the case should be reported immediately and active treatment should be carried out.