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Sexually transmitted infection

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noun, plural: sexually transmitted infections

(pathology) A type of infection that is primarily spread by sexual contact


A sexually transmitted infection (STI) is a type of infection wherein the (bacterial, viral, or protozoan) causative agent is contracted by sexual contact (e.g. by vaginal intercourse, anal sex, or oral sex). The infection with the causative agent may or may not produce symptoms. The STI may progress into a disease, which in this case is referred to as sexually transmitted disease or STD.

There are more than thirty pathogens that cause STIs. Some of these bacterial species include Chlamydia trachomatis (causing chlamydia infection), Neisseria gonorrhoeae (causing gonorrhea), and Treponema pallidum (causing syphilis). Viral species include Human immunodeficiency virus (causing HIV/AIDS), herpes simplex virus (causing genital herpes), and human papillomavirus (causing genital warts). Trichomonas vaginalis is a protozoan that causes trichomoniasis. Non-sexual mode of transmission may be through blood transfusion with contaminated blood and tissues, breastfeeding, or at childbirth.

Abbreviation / Acronym:

  • STI


  • venereal disease

See also: