Acquiring relevant information shows that the reason for the outbreak in Cangzhou City is that symptoms appeared late and were relatively mild after infection. Some people were infected due to factors such as late onset of symptoms and relatively mild symptoms after infection. This situation increased the difficulty of epidemic detection, which resulted in more and more epidemics in Cangzhou City. Therefore, the reason for the outbreak in Cangzhou City was that symptoms appeared after infection. Reasons for late symptoms and relatively mild symptoms.