AIDS is a category B infectious disease. There are 39 types of infectious diseases, including infectious diseases in category A, infectious diseases in category B, and infectious diseases in category C. There are two types of infectious diseases in category A, including plague and cholera. AIDS, syphilis, gonorrhea, rabies, diphtheria, scarlet fever and 26 other infectious diseases belong to category B. Category C infectious diseases include 11 types of influenza A, mumps, leprosy, etc. The ways of transmission of AIDS include sexual transmission, blood transmission, and vertical transmission from mother to child. Always wear a condom when having unsafe sex. When exposure occurs during contact with a person with HIV, be sure to actively intervene for treatment. Pregnant women who test positive for HIV must have regular checkups and aggressive interventions.