The four infections refer to Hepatitis B, Hepatitis C, Syphilis, and AIDS. Hepatitis B is mainly transmitted through blood, body fluids, and mother-to-child vertical transmission. Hepatitis B primary screening is mainly to check the hepatitis B surface antigen, if the hepatitis B surface antigen is positive, you should further check the hepatitis B virus HBV-DNA.Hepatitis C is mainly transmitted through blood and body fluids, and the primary screening of hepatitis C is mainly to check the hepatitis C antibody and hepatitis C HCV-RNA test. Syphilis is mainly transmitted through sexual intercourse and can be diagnosed through syphilis spirochete testing. HIV is mainly transmitted through blood, body fluids and sexual intercourse, and can be initially screened by testing for HIV antibodies. If positive, further testing is needed to confirm the diagnosis.