According to the outbreaks and epidemics of infectious diseases and the degree of harm they cause, infectious diseases are categorized into categories A, B and C. The most common infectious diseases are the plague and cholera. Among them, there are two types of category A infectious diseases, including bubonic plague and cholera. Category B infectious diseases include H7N9 avian influenza, malaria, schistosomiasis, leptospirosis, syphilis, gonorrhea, brucellosis, scarlet fever, neonatal tetanus, diphtheria, whooping cough, epidemiological cerebrospinal meningitis, typhoid fever and paratyphoid fever, pulmonary tuberculosis, bacterial amebic dysentery, anthrax, dengue fever, epidemiological encephalitis B, rabies, epidemiological hemorrhagic fever, measles, human infection with highly pathogenic avian influenza, poliomyelitis, and other infectious diseases. Avian influenza, poliomyelitis, viral hepatitis, AIDS, and infectious atypical pneumonia. Category A infectious diseases are more contagious and may cause widespread epidemics and outbreaks, which may lead to many deaths and may have a great impact on the national economy and the safety of individual lives. Category B infectious diseases are also more contagious, but the lethality rate is not very high, compared to Category A infectious diseases, and will not lead to widespread scale of deaths and outbreaks of epidemics. The detection of Category A and B infectious diseases should be promptly reported in accordance with the policy and preventive and control measures should be taken to minimize their impact.