Sexually transmitted infections can be caused by:

  • Bacteria (gonorrhea, syphilis, chlamydia)
  • Parasites (trichomoniasis)
  • Viruses (human papillomavirus, genital herpes, HIV)

Sexual activity plays a role in spreading many other infectious agents, although it's possible to be infected without sexual contact. Examples include the hepatitis A, B and C viruses, shigella, cryptosporidium and Giardia lamblia.

Feb. 23, 2013