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Sexually transmitted infection
Synonyms Sexually transmitted diseases (STD), venereal diseases (VD)
Syphilis is a dangerous disease.png
"Syphilis is a dangerous disease, but it can be cured." Poster encouraging treatment. Published between 1936 and 1938.
Specialty Infectious disease
Symptoms None, vaginal discharge, penile discharge, ulcers on or around the genitals, pelvic pain[1]
Complications Infertility[1]
Causes Infections commonly spread by sex[1]
Prevention Not having sex, vaccinations, condoms[2]
Frequency 1.1 billion (STIs other than HIV/AIDS, 2015)[3]
Deaths 108,000 (STIs other than HIV/AIDS, 2015)[4]

Sexually transmitted infections (STI), also referred to as sexually transmitted diseases (STD) or venereal diseases (VD), are infections that are commonly spread by sexual activity, especially vaginal intercourse, anal sex and oral sex. Many times STIs initially do not cause symptoms. This results in a greater risk of passing the disease on to others. Symptoms and signs of disease may include vaginal discharge, penile discharge, ulcers on or around the genitals, and pelvic pain. STIs can be transmitted to an infant before or during childbirth and may result in poor outcomes for the baby. Some STIs may cause problems with the ability to get pregnant.

More than 30 different bacteria, viruses, and parasites can be transmitted through sexual activity.[1] Bacterial STIs include chlamydia, gonorrhea, and syphilis.[1] Viral STIs include genital herpes, HIV/AIDS, and genital warts.[1] Parasitic STIs include trichomoniasis.[1] While usually spread by sex, some STIs can be spread by non-sexual contact with donor tissue, blood, breastfeeding, or during childbirth.[1] STI diagnostic tests are usually easily available in the developed world, but this is often not the case in the developing world.[1]

The most effective way of preventing STIs is by not having sex.[2] Some vaccinations may also decrease the risk of certain infections including hepatitis B and some types of HPV.[2] Safer sex practices such as use of condoms, having a smaller number of sexual partners, and being in a relationship where each person only has sex with the other also decreases the risk.[1][2] Circumcision in males may be effective to prevent some infections.[1] During school, comprehensive sex education may also be useful.[9] Most STIs are treatable or curable.[1] Of the most common infections, syphilis, gonorrhea, chlamydia, and trichomoniasis are curable, while herpes, hepatitis B, HIV/AIDS, and HPV are treatable but not curable.[1] Resistance to certain antibiotics is developing among some organisms such as gonorrhea.[10]

In 2015, about 1.1 billion people had STIs other than HIV/AIDS.[3] About 500 million were infected with either syphilis, gonorrhea, chlamydia or trichomoniasis.[1] At least an additional 530 million people have genital herpes and 290 million women have human papillomavirus.[1] STIs other than HIV resulted in 108,000 deaths in 2015.[4] In the United States there were 19 million new cases of sexually transmitted infections in 2010.[11] Historical documentation of STIs date back to at least the Ebers papyrus around 1550 BC and the Old Testament.[12] There is often shame and stigma associated with these infections.[1] The term sexually transmitted infection is generally preferred over sexually transmitted disease or venereal disease, as it includes those who do not have symptomatic disease.[13]