Novel coronavirus incubation period is contagious, and most infectious diseases become contagious in the late incubation period, making it difficult to completely control infectious diseases. When contacting a person with latent infection without symptoms of respiratory infection such as fever and cough, although the other party has no symptoms, but already has infectious, contact with it may still be infectious, whether it is infectious, mainly depending on whether the respiratory secretions contain virus. In addition, after the observation of patients with novel coronavirus pneumonia found that close contact with a confirmed infected person, after 2-14 days of observation period without symptoms, their pharyngeal swab test has appeared positive for nucleic acid, suggesting that there is a virus in the respiratory secretions. In practice, it was also found that some patients did not come into contact with patients with real symptoms of infection, but only with those in the latent phase of infection and caused transmission. Therefore, since the latent phase of novel coronavirus pneumonia is infectious, the risk of infection should not be judged by the presence or absence of symptoms in the other person, but rather by the later stage of the infection. Once the other party is diagnosed with the infection at a later stage, even if there are no symptoms during the contact period, there is still a risk of being infected, and self-isolation and observation should be done. Content source: Dr. You Lai