New crown reactivation may be contagious, so measures such as isolation and observation need to be continued. The so-called return to positive nucleic acid test refers to the manifestation of two consecutive negative nucleic acid tests of a newly infected person who has undergone centralized quarantine or treatment in a designated hospital, and then shows positive nucleic acid test results again after being released from quarantine or hospitalization. While a positive nucleic acid test mainly means that fragments of the New Crown virus are found in the sample, and it is not possible to directly define whether it is infectious or not. Nucleic acid testing is done to detect fragments of the virus, and the detection of a positive nucleic acid fragment does not mean that a live virus has been detected. After culturing the viruses in the patient’s body, experts sequenced the genes of these viruses, and the results showed that the viruses in the bodies of some patients are “dead viruses”, that is, after the death of the virus, the “corpse” fragments remain in the body to form gene fragments, which do not necessarily have the ability to be infectious. It is not necessarily infectious. Therefore, after the resurgence of the virus, it is necessary to continue to implement the isolation measures, and at the same time, carry out procedures such as re-examination and expert group validation, and then handle the case in accordance with the requirements. During the new crown epidemic, it is recommended that everyone should still take good personal protection to avoid the spread of the epidemic.