Sexually transmitted infections (STIs), also commonly called sexually transmitted diseases (STDs), are infections passed through vaginal, oral, or anal sex. Many can have an STI unknowingly if they are asymptomatic (without symptoms) or exhibit mild symptoms. Screening is essential for diagnosing, treating, and preventing further spread. 

Sexually transmitted infections are quite common in the United States (U.S.), and rates have increased steadily, with millions of new infections occurring yearly. According to a recent Centers for Disease Control and Prevention surveillance report on STIs, over 2 million chlamydia, gonorrhea, and syphilis cases were reported in 2020.

This article reviews the latest statistics on the most common STIs and discusses how to reduce your risk.

How Many People Have STIs?

In 2018, the CDC estimated that one in five people in the U.S., or 20% of the population, had a sexually transmitted infection (STI). These STIs include chlamydia, gonorrhea, syphilis, hepatitis B, herpes simplex virus type 2, human immunodeficiency virus (HIV), human papillomavirus (HPV), and trichomoniasis.

Most Common STIs

Chlamydia, gonorrhea, and syphilis are the most commonly notifiable sexually transmitted infections in the U.S. Though HIV is more common than gonorrhea or syphilis, it is often considered its own category of disease.

STI vs STD: What’s the Difference?

The terms “sexually transmitted infection” and “sexually transmitted disease” are often interchangeable. An infection occurs when the bacteria or virus is sexually transmitted, and may or may not cause symptoms. When the infection causes symptoms or other complications, it becomes a sexually transmitted disease.

Chlamydia

Chlamydia was the most common notifiable STI in the U.S. in 2020. It is most prevalent among adolescents and young adults between 15 and 24 and transmitted through oral, vaginal, or anal sex, as well as passed from an infected mother to a baby during childbirth.

Notifiable STIs are STI cases that healthcare facilities must report to the government or health authorities.

Chlamydia is often asymptomatic; when symptoms are present, it’s usually five to 14 days after infection. Symptoms of chlamydia include:

  • Abnormal dischargeBurning when peeing Pain or swelling of the testicles (in men)

Symptoms of a rectal chlamydia infection include:

  • Pain DischargeBleeding

Chlamydia is a treatable STI; your healthcare provider can prescribe medicine and monitor for repeated infection. If left untreated, chlamydia can cause permanent damage to women’s reproductive organs and make it more challenging for them to get pregnant.

Gonorrhea

The second most common notifiable STI in the U.S. is gonorrhea, which can cause infection in the genitals, rectum, and throat. Young people ages 15 to 25 are disproportionately affected. Like chlamydia, it’s transmitted through oral, vaginal, or anal sex and can be passed down during childbirth. 

Gonorrhea is often asymptomatic. Symptoms of gonorrhea, when present, include:

  • Pain or burning when peeing Vaginal discharge and bleeding between periods (in women)White, yellow, or green penile discharge (in men)Painful or swollen testicles (in men)

Symptoms of gonorrhea in women may be confused with a bladder or vaginal infection.

Symptoms of rectal gonorrhea infection include:

  • DischargeItchingSorenessBleedingPain during bowel movements

Gonorrhea can lead to health complications if left untreated; women can develop pelvic inflammatory disease, and men can develop pain and potential infertility. Gonorrhea is treatable; a healthcare provider can prescribe medicine to cure the infection. 

Syphilis

Syphilis is the third most common notifiable STI in the U.S., with rates increasing nearly every year since 2001. Syphilis spreads through contact with syphilis sores during vaginal, anal, or oral sex.

A mother can also spread syphilis to her baby during pregnancy, which is called congenital syphilis. In 2020, 149 stillbirths and infant deaths were attributed to congenital syphilis.

Syphilis has four stages: primary, secondary, latent, and tertiary; symptoms vary by stage. Syphilis stages include:

  • Primary stage: One or more sores in, on, or around the penis, vagina, anus, rectum, and lips or mouth
  • Secondary stage: Skin rash or sores in the mouth, vagina, or anus, rough, red, or a reddish-brown rash most commonly in the palm of the hands or bottoms of the feet (but can appear anywhere), fever, swollen lymph glands, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue
  • Latent stage: No visible symptoms
  • Tertiary stage: Can affect organ systems, but most people do not develop this stage

Syphilis is treatable with antibiotics. Left untreated, syphilis can affect the brain, nervous symptoms, eyes, or ears.

STI Statistics

The below statistics represent the STI surveillance data collected during COVID-19 in 2020. Health authorities advise interpreting the data cautiously, as the pandemic has affected screening and data collection.

  • 1.6 million cases of chlamydia were reported, a 13% decrease from 201961% of all cases were among adolescents and young adults (15 to 24 years old)

  • 677,769 cases of gonorrhea were reported, a 5.7% increase from 2019

  • 133,945 cases of syphilis and 2,148 congenital syphilis were reported, up 6.8% and 15% from 2019

STI Prevention

All sexually transmitted infections are preventable and treatable, and some are curable. Testing can help with timely treatment and prevent spreading the infection to others.

The COVID-19 pandemic affected screening and surveillance for STIs. A strained health system and the closures of clinics made it challenging to test, diagnose, and gather surveillance data on STIs. Despite the pandemic, the CDC’s 2020 surveillance report on STDs reported 2.4 million chlamydia, gonorrhea, and syphilis cases.

The steep rise in congenital syphilis is reflective of the syphilis epidemic. Congenital syphilis most commonly occurs when the mother doesn’t receive timely prenatal care or syphilis testing.

There are disparities in rates of reported STIs:

The Importance of Prevention

STI rates are increasing and adolescents, young adults, and men who have sex with men are at an increased risk. Additionally, having a sexually transmitted infection places people at a higher risk for HIV.

Prevention can avoid irreversible health complications, including:

  • Reproductive problems Fetal and perinatal complicationsCancerFacilitation of HIV transmission

How to Prevent STIs

There are several ways to prevent STIs, including:

  • Abstinence from vaginal, oral, and anal sex
  • Vaccination to prevent hepatitis and HPV
  • Reducing your number of sexual partners
  • Regularly getting tested and sharing results with sexual partners
  • Using male, latex condoms or female condoms correctly and consistently during oral, anal, and vaginal sex
  • Practicing monogamy (a long-term, mutually exclusive relationship with one partner)

Summary

Rates of sexually transmitted infections (STIs) are rising in the U.S., especially among adolescents and young adults. Individuals with STIs like chlamydia and gonorrhea can be asymptomatic, so taking measures to prevent contracting and spreading STIs is important.

STIs are preventable and treatable but may lead to serious complications if left untreated. 

A Word From Verywell

If you have concerns or think you may have symptoms of an STI, talk to your healthcare provider about getting screened. All STIs are treatable, and many are curable. Early treatment can avoid further complications in the future.

Frequently Asked Questions

  • What percentage of the population has an STI?
  • About one in five people (or 20% of the population) had a sexually transmitted infection in 2018.
  • Where are STI rates the highest?
  • According to the CDC’s 2020 surveillance report on STIs, the southern U.S. seems hardest hit by STIs. Cities with large populations of Hispanic and non-Hispanic Black people are also disproportionately affected, suggesting systemic inequalities that restrict access to healthcare and testing.
  • Do females or males have a higher risk of contracting an STI?
  • Women disproportionately bear the long-term consequences of STIs. Though women tend to have fewer symptoms of common STIs, like chlamydia and gonorrhea, symptoms may be mistaken for other health conditions, like a yeast infection, and not adequately treated. Additionally, the lining of the vagina is much thinner and conducive for bacteria and viruses to infiltrate and grow.

About one in five people (or 20% of the population) had a sexually transmitted infection in 2018.

According to the CDC’s 2020 surveillance report on STIs, the southern U.S. seems hardest hit by STIs. Cities with large populations of Hispanic and non-Hispanic Black people are also disproportionately affected, suggesting systemic inequalities that restrict access to healthcare and testing.

Women disproportionately bear the long-term consequences of STIs. Though women tend to have fewer symptoms of common STIs, like chlamydia and gonorrhea, symptoms may be mistaken for other health conditions, like a yeast infection, and not adequately treated. Additionally, the lining of the vagina is much thinner and conducive for bacteria and viruses to infiltrate and grow.