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What Is The Most Common Sexually Transmitted Infection (STI)?

This article was reviewed for accuracy by Dr. Kirti Patel, MD, MHL a board-certified gynecologist at UMass Memorial Healthcare and the Chief Medical Officer of The POV.


It is estimated that one in two sexually active Americans will contract an STD by the age of 25.


Chlamydia is the most commonly reported sexually transmitted infection (STI) in the United States. In 2020, 1,538,561 cases of chlamydia were reported to the Centers for Disease Control and Prevention (CDC). However, it's estimated that as many as 2.86 million people are infected with chlamydia each year. This discrepancy is due to a lack of symptoms in many people who have chlamydia.


The CDC reports that chlamydia affects an estimated 2.9 million people in America every year, making it much more prevalent than gonorrhea or syphilis. It's also important to note that not everyone who has chlamydia has symptoms—so if you're concerned about this STI, make sure you get tested regularly!


Some people may not realize they have an infection and may not go to their doctor or get tested regularly. While chlamydia is treatable and curable with antibiotics, it can cause severe complications if left untreated — including infertility. The best way to protect yourself from STIs is by using condoms correctly during sex and getting tested regularly.


What Is Chlamydia?


Chlamydia is a bacterial infection caused by the bacterium Chlamydia trachomatis. It's one of the most common STIs in the United States, and can be passed between partners through unprotected vaginal, anal, or oral sex. It's especially dangerous for women because it can cause pelvic inflammatory disease (PID) and infertility if left untreated.


Chlamydia can also be passed to newborns during childbirth if their mothers have chlamydia when they give birth; this is called mother-to-child transmission (MTCT).



How Is Chlamydia Transmitted?


Chlamydia is a common STI that can be passed between partners through unprotected vaginal, anal, or oral sex. It can also be passed to a baby during childbirth.


It's estimated that chlamydia affects about 4 million people in the United States each year. The infection is most common in people ages 15-24 and women of any age who have new or multiple sex partners. Anyone with a vagina younger than 25 accounts for about half of all reported cases of chlamydia each year, this could be because they're more likely to have an asymptomatic infection (meaning they don't show symptoms) and therefore don't get tested or treated right away.


If you think you might have been exposed to chlamydia but haven't gotten tested yet, talk with your healthcare provider about getting tested as soon as possible so they can diagnose it before any long-term health effects start showing up—and get treated immediately if necessary.


An infected person may pass on the bacteria without realizing it if their partner is also carrying the bacteria somewhere else on their body, like their throat or rectum. This means that someone with an active case might re-infect themselves even after being cured if their partner also has chlamydia and isn't being treated for it properly yet.



Symptoms of Chlamydia


Symptoms of chlamydia can include discharge from the vagina or penis, burning while urinating, and pain in the lower abdomen. These symptoms may not be present in all people.


If you suspect that you have chlamydia, it's important to see a doctor right away. You may not exhibit symptoms of the infection at first, and if left untreated, it can lead to severe health problems, including infertility.


If you do have some of these symptoms (which are often mistaken for other conditions), they're likely milder than what will happen if the infection isn't treated:


  • Discharge from the vagina or penis


  • Abdominal or pelvic pain


  • Burning while urinating


  • Abnormal bleeding


  • Pain with sex


Chlamydia is often mistaken for other conditions, such as a bladder infection or yeast infection. If you have more than one sexual partner you should get tested for STIs on a regular basis even if you do not notice any symptoms of an STI because most infections are asymptomatic.



Treatments for Chlamydia


Chlamydia is treated with antibiotics for the patient and all recent sexual partners. Treatment should be done even if the symptoms are mild or absent.


If you have been diagnosed with chlamydia you should avoid having sex until all your sexual partners have completed their antibiotic regimen and test negative since they could pass on this infection through sex or close contact such as kissing or intimate body contact


Using condoms and getting regular testing are important to prevent and treat chlamydia. Condoms can reduce the risk of STIs, and getting tested regularly is important to prevent and treat STIs, including chlamydia.



Where Can I Get Tested for Chlamydia and Other STIs?


If you’re sexually active, it’s important to get tested regularly for STIs. You can talk to your doctor about which tests are appropriate for you, but most healthy sexually active people over age 13 should get tested at least once a year—although more often is better. The sooner you find out if you have an STI, the sooner you can start treatment and avoid complications.


To get tested for chlamydia, you can visit:


  • A doctor's office


  • A sexual health clinic


  • Your local drugstore (for OTC testing kits)


  • A pharmacy (like Walgreens or CVS can provide testing and OTC testing kits)


  • A health clinic (like Planned Parenthood)


  • A family planning clinic or family doctor



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