อ้างอิง [1] WHO Key facts 28 Feb 2019 [2] ECDC EUROPE [3] Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention [4] Gift, Thomas L. et al. Sex Tran Dis: April 1999 - Volume 26 - Issue 4 - p 232240