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    Infectious Diseases A-Z: What is an STI?

a young couple in bed, looking sad or upset
An estimated 20 million new sexually transmitted infections (STIs) occur in the U.S. each year, according to The Centers for Disease Control and Prevention. You may be hearing the term sexually transmitted infection used more, instead of sexually transmitted disease (STD). Dr. Stacey Rizza, a Mayo Clinic infectious diseases specialist, explains why there's a change in the language and what it means.

Watch: Dr. Stacey Rizza explains STIs.

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"The term we use in medicine is STI, which stands for sexually transmitted infection," says Dr. Rizza. "The older term was STD, which stood for sexually transmitted disease, but all of these are caused by infections. And that’s why we use the newer term STI."

Dr. Rizza says an STI is not just one type of infection. "It can be a bacteria, or it can be a virus that is transmitted through a sex act, and that can be oral sex, vaginal sex or anal sex."

There are many different STIs transmitted through bacteria and viruses. Three common STIs in the U.S. are syphilis, gonorrhea and chlamydia. Left untreated, these infections can have long-term effects.

"In the case of chlamydia and gonorrhea in young women, it can cause chronic infections that lead to pelvic inflammatory disease and sometimes even infertility," says Dr. Rizza. "So that’s why it’s very important not only that we identify whether or not they’re infected, but treat them right away so they don’t transmit the infection to others, and they don’t have long-term effects themselves."

"Syphilis is another STI that’s caused by a bacteria where these numbers have been going up in the U.S. every year as well," says Dr. Rizza. "And syphilis can cause some very significant long-term consequences if it’s not diagnosed and treated early on. Those are wide-ranging, from cardiovascular problems, to problems with the brain, to skin problems, and all sorts of other implications."

Dr. Rizza urges people to get screened for STIs and if necessary, get treated. She also says using condoms or barrier protection when having sex is the safest way to prevent the spread of STIs.