Two negative nucleic acid tests but fever in a neocoronazid subcloser is not enough to completely rule out fever due to novel coronavirus infection, but may also be due to other causes. 1. Novel coronavirus infection: One of the common manifestations of novel coronavirus infection is fever, and if the nucleic acid test for novel coronavirus is positive, the diagnosis is usually clear. However, some people may have false-negative results, and there have been many cases in which a person who tested negative for novel coronavirus nucleic acid has turned positive during isolation. Therefore, if a febrile patient has an epidemiologic history associated with novel coronavirus infection, a chest CT consistent with features of novel coronavirus pneumonia, etc., close observation is needed even if two novel coronavirus nucleic acid tests are negative. 2. Other causes: such as common cold, tuberculosis, and other infections such as urinary tract infections, biliary tract infections, etc., can also cause fever, and the results of novel coronavirus nucleic acid test are usually negative, and such cases may also occur. In addition, many non-infectious diseases can cause fever, including cryptogenic opportunistic pneumonia and hyperthyroidism, which may also occur in patients who have a negative novel coronavirus nucleic acid test. [Note: In this article, “new coronary pneumonia and new coronary virus pneumonia” were renamed to “new coronary virus infection” on December 26, 2022, as announced by the National Health Commission.