Angelica Bottaro is a writer with expertise in many facets of health including chronic disease, Lyme disease, nutrition as medicine, and supplementation. 

Lauren Schlanger, MD, is a board-certified primary care physician with a focus on women's and transgender health.

Chlamydia is a sexually transmitted infection (STI) that often presents without symptoms. People between the ages of 15 and 24 are the most likely to contract the infection. Roughly two-thirds of chlamydia cases are found in people that belong to that age group.

This article discusses facts and statistics that you should know about this STI.

Chlamydia is a common STI that is caused by the bacterium Chlamydia trachomatis . It is often asymptomatic, meaning there are no symptoms after a person contracts it. People may be unaware that they have symptoms, making it easier to spread.

Although chlamydia can be cured, if left untreated, it can lead to harmful sexual health consequences, especially for people with a uterus.

There were 1.5 million new cases of chlamydia in 2020. That amounts to roughly 481.3 cases per 100,000 people. Because of the numbers documented, chlamydia was the most reported STI in the United States in 2020.

While those numbers seem high, they are actually lower than the prior year. The year 2020 saw a 13% decrease in reported cases from 2019.

The incidence rate of chlamydia continuously rose between 2000 and 2019 before declining between 2019 and 2020. In the year 2000, rates were roughly 250 cases per 100,000 people in the country. By 2019, those rates had risen to just over 500 cases per 100,000 people.

A 2019 press release from the Centers for Disease Control and Prevention (CDC) reported that the rising rates of chlamydia and other STIs can be attributed to:

Cases of chlamydia do not affect all ethnicities in the same way. There is a large disparity in terms of which communities are more often affected by the STI.  This is not due to genetics but rather to a number of reasons, including access to health care, economic disadvantage, and other barriers to the use of services.

The most affected ethnicities and the rate at which they are more likely to contract chlamydia are:

The overall rates of chlamydia by sex vary depending on the age group. That said, roughly 61% of chlamydia cases in both sexes combined are found in people between the ages of 15 and 24 with people with uteruses in this age group being the most affected.

According to the CDC, roughly 1 in 20 people with uteruses who are sexually active between the ages of 14 and 24 have this STI.

As people continue to age, the numbers become steady among sexes. In people more than 39 years old, people with a penis account for more chlamydia cases than people with a uterus.

The cause of chlamydia is the bacterium known as Chlamydia trachomatis. This bacterium is easily spread through unprotected sexual contact.

The chance of acquiring chlamydia rises with the following factors:

A person who engages in any sexual activity—whether genital, anal, or oral—can be exposed to and contract a chlamydia infection.

While chlamydia isn’t necessarily fatal, having an untreated infection can lead to severe health consequences. For people with vaginas and uteruses, not getting prompt treatment can cause irreversible damage to the reproductive system and conditions such as:

In people with penises and testicles, untreated chlamydia can lead to:

As many as 40% of untreated chlamydia cases lead to PID.

About 70% of people with uteruses and 50% of people with penises won’t experience symptoms of chlamydia. Because of this, screening and early detection are vital to reduce the risk of more severe health consequences.

According to the CDC, people with a uterus younger than 25 years old and those older than 25 who have multiple sexual partners should get tested yearly for chlamydia. Men who have sex with men (MSM) should also be tested annually.

The CDC recommends people with multiple partners and those who have anonymous sex get tested every three to six months.

The method for diagnosing chlamydia varies. People with vaginas will have a sample of fluid taken from the vagina, cervix, rectum, or throat using a swab. People with penises are tested with a urine sample or swab from the rectum or throat.

These tests are highly reliable, and there is little chance of a false-positive result (when the test indicates you have chlamydia when you actually do not). In some cases, a urine sample is used to detect chlamydia.

Chlamydia is a highly common STI that affects a large number of the American population. Roughly 1.5 million cases were reported to the CDC in 2020 alone. While the numbers have steadily increased since 2000, the cases dropped slightly between 2019 and 2020.

People with a uterus, Black Americans, and people between the ages of 15 and 24 are among the most affected populations. While people with a uterus are more likely to be diagnosed with chlamydia, as people age, the roles reverse and people with a penis over the ages of 40 account for more cases in that age group.

The biggest risk factors associated with the spread of infection is having condomless sex with someone who has the infection. Having multiple partners can also increase the risk. Not having proper access to healthcare screenings may also play a role in the transmission of the infection.

While chlamydia isn’t fatal, it can lead to dire health consequences, especially for people with a uterus. People in this group with an untreated chlamydia infection can develop various gynecological issues, all of which can affect fertility.

Having chlamydia often comes with a stigma attached. People often frown upon STIs. The stigma isn’t warranted, considering how incredibly common chlamydia is.

The good news surrounding chlamydia is that, even if you contract it, it is easily treatable with antibiotics. With such a high number of cases, the best thing you can do is practice safer sex and get screened at least once a year or more frequently, depending on your risk factors.

Typically, a chlamydia test is quick and easy. Urine tests, as well as swab tests, can be done to detect the chlamydia bacterium. Swab tests can be used to detect chlamydia in the genitals, rectum, or oral cavity.

If you receive a positive result, don’t panic. Treatment is easy and highly effective. Once you receive the positive result, your medical provider will write you a prescription for antibiotics and instruct you on how to take them. You will also be asked to notify all previous sexual partners as well.

First and foremost, you can practice safe sex. Regardless of how many partners you choose to have, safer-sex practices—such as wearing condoms—can significantly decrease your risk of contracting this and other STIs. Discussing your testing status with partners beforehand can also help to reduce your risk.

Centers for Disease Control and Prevention. Chlamydia - CDC basic fact sheet.

Centers for Disease Control and Prevention. Sexually transmitted disease surveillance 2020 national overview.

Centers for Disease Control and Prevention. Sexually transmitted disease surveillance 2019 - national overview.

Centers for Disease Control and Prevention. Reported STDs reach all-time high for 6th consecutive year.

Centers for Disease Control and Prevention. Sexually transmitted disease surveillance 2019: Table 11N. Chlamydia - rates of reported cases by race*/Hispanic ethnicity, age group, and sex, United States, 2019.

Jones J, Weiss K, Mermin J, Dietz P, Rosenberg ES, Gift TL, Chesson H, Sullivan PS, Lyles C, Bernstein KT, Jenness SM. Proportion of incident human immunodeficiency virus cases among men who have sex with men attributable to gonorrhea and chlamydia: a modeling analysis. Sex Transm Dis. 2019 Jun;46(6):357-363. doi:10.1097/OLQ.0000000000000980

Nadeau C, Fujii D, Lentscher J, Haney A, Burney RO. The gynecologic health consequences of chlamydia trachomatis infection in military servicewomen. Semin Reprod Med. 2018 Nov;36(6):340-350. doi:10.1055/s-0039-1678752

Malhotra M, Sood S, Mukherjee A, Muralidhar S, Bala M. Genital chlamydia trachomatis: an update. Indian J Med Res. 2013 Sep;138(3):303-316.

Centers for Disease Control and Prevention. Sexually transmitted diseases: Which STD tests should I get?

Center for Disease Control and Prevention. National overview of STDs, 2020.

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