What are the three most common STIs and what impact do they have in the U.S.?

The most common STIs are chlamydia, gonorrhea, and syphilis. These three diseases are responsible for about 4.3 million infections per year in the United States. Each of these STIs is very different in terms of the type of agent and type of infection that it causes. Chlamydia is the most commonly reported STI in the United States. Caused by the bacterium Chlamydia trachomatis, chlamydia is known as a "silent" disease because the majority of infected people exhibit no symptoms. Chlamydia can damage a woman's reproductive organs and, if untreated, can cause infertility.
Gonorrhea is almost as common as chlamydia and is also caused by bacteria that can grow easily in a woman's reproductive tract, both men and women's urethras, as well as a person's mouth, throat, eyes, and anus. The symptoms for gonorrhea may be mild and can be mistaken for urinary tract infections, although most women do not experience any symptoms. Anyone having sex is at risk for acquiring an infection, and an untreated pregnant woman can spread it to her baby during childbirth. Chlamydia and gonorrhea are particularly common among adolescents and young adults.

Syphilis is another STI caused by a bacterium, but it can cause long-term complications or death if left untreated or if treated inadequately. Although less common than chlamydia and gonorrhea, syphilis is a public health concern. Syphilis is contracted through direct contact with sores and through sexual contact with an infected person, as well as from mother to child during childbirth. Syphilis is particularly prevalent among men who have sex with men, who comprise 67% of all cases.

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