A Guide to Chlamydia

A Guide to Chlamydia

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Understanding Chlamydia

Chlamydia is one of the most common sexually transmitted infections (STIs) in the world.1 While this disease is easily treatable, it can have serious health consequences if untreated.1 This blog is an in-depth look at: chlamydia infection and its origins; how it is spread; the consequences of infection; what tests and treatments are available; how to prevent infection; and what you can do if you think you may be infected.

Hologic: A Leader in STI Testing

Hologic is a medical diagnostics company that provides highly accurate testing for chlamydia and other STIs. Hologic scientists have developed molecular tests that determine whether or not you have chlamydia infection with great certainty. Hologic works toward the goal of stopping the spread of chlamydia and other STIs so that people can avoid the long-term health consequences of these infections.

Where Did Chlamydia Come From?

Chlamydia is the name for the infection caused by a pathogenic bacteria called Chlamydia trachomatis. It was first discovered in 1907 by scientists Halberstaedter and von Prowazek, who discovered the bacteria in the conjunctiva, a part of the eye.2 There are 9 species included in the genus Chlamydia, and C. trachomatis is one.3 While the origins of C. trachomatis as an STI are uncertain, it is likely that the disease evolved with humans and evolved from a bacterium existing 700 million years ago.3 Until the mid-1990s, highly sensitive chlamydia testing did not exist.4

How Common is Chlamydia?

Chlamydia is the most common bacterial STI in the world.5 Estimates from the World Health Organization (WHO) show that 131 million new chlamydia infections occur each year, with 4.2% of the population infected.6

In the United States, the infection affects an even higher percentage of the population, at 4.79%.7 In the U.S. in 2015, 1,526,658 cases of chlamydia were reported, and approximately 3 million new cases are estimated to occur each year.8,9

Several groups are disproportionately affected by chlamydia. Women are disproportionately affected by chlamydia in the U.S., with twice the number of infections in men.9 Younger people in the U.S. experience the brunt of infection, with 65% of cases in patients age 15-24.7 The disease is also common among men who have sex with men (MSM) and certain racial and ethnic groups.1

How Does Chlamydia Spread?

Chlamydia is contracted through vaginal, anal or oral sexual contact or via contact with semen or vaginal fluid.10 The infection may be transmitted during sex even if a person does not ejaculate.1 It may also be contracted by using sex toys shared with an infected person.11 In addition to sexual contact, chlamydia can be passed from a mother to her baby during childbirth.1

Chlamydia can infect the tissues that line our body cavities1:

  • Urethra
  • Vagina
  • Cervix
  • Fallopian tubes
  • Anus
  • Rectum
  • Inside of the eyelid
  • Throat

Chlamydia can be present and spread from one person to another even if he or she has no symptoms.1 Abstinence, or refraining from sex entirely, eliminates the possibility of contracting chlamydia in adults, and the use of condoms greatly reduces the risk of infection.1 In addition, being in a long-term, monogamous relationship with someone who has tested negative for chlamydia reduces the risk of contracting the STI during sex.1

People with multiple sex partners in the past year, those with a history of STIs, people who inconsistently use condoms and people age 24 and younger have an increased risk for contracting chlamydia.1 Women with cervical ectopy, in which cells from the inside of the cervix appear on the outside of the cervix, may also have increased risk of contracting chlamydia.1 Men who have sex with men have an increased risk as well.8

What Are the Symptoms of Chlamydia?

Chlamydia infection is commonly asymptomatic in men and women – as many as 75% show no symptoms of infection.12 The majority of the time, chlamydia infection causes no symptoms.12 Symptoms may not appear until several weeks after exposure.1

Even without the presence of symptoms, this infection can cause long-term damage, so testing and treatment is important. When symptoms are present in women, they include8:

Chlamydia Symptoms in Women1,13

  • Unusual vaginal discharge
  • Bleeding between periods
  • Pus in urine
  • Pain during urination
  • Frequent urination
  • Abdominal or pelvic pain or tenderness
  • Rectal pain, discharge or bleeding
  • Fever
  • Nausea
  • Pain during sex

Chlamydia Symptoms in Men1

  • Penile discharge
  • Pain during urination
  • Pain and swelling in the testicles
  • Rectal pain, discharge or bleeding

Health Consequences of Chlamydia

When a person is first infected with chlamydia, he or she may experience some immediate consequences. Initial consequences include physical discomfort from symptoms (if present) and mental or emotional discomfort about the diagnosis and stigma attached to STIs.1

Consequences in Women

More serious, long-term consequences can also result from untreated chlamydia infection. Most significantly, chlamydia in women can result in pelvic inflammatory disease (PID).14 PID is caused when certain bacteria (germs) move up from the vagina and cause infection in other reproductive organs.14 More than 1 million women are diagnosed in the U.S. with PID each year.14

Pelvic Inflammatory Disease

Without treatment, approximately 10-15% of untreated chlamydia cases result in PID.15 PID can lead to other serious consequences:

  • Infertility (inability to become pregnant)
    • 20% of PID-infected women become infertile.16
  • Scar tissue inside and outside of fallopian tubes17
    • Fallopian tubes can become blocked and cause further complications.
  • Ectopic pregnancy (pregnancy that occurs outside of the womb)17
    • This can cause fallopian tube rupture, leading to life-threatening blood loss.
    • Ectopic pregnancy embryos cannot survive.
  • Chronic (long-term) pelvic pain
    • 18% of PID-infected women have chronic pelvic pain.17
  • Fitz-Hugh-Curtis Syndrome
    • Also known as perihepatitis, this syndrome is marked by inflammation of the liver capsule and surrounding peritoneum causing pain.1

While PID can be cured with antibiotics, they will not reverse any long-term damage that has already occurred as a result of a long-term infection.1

Complications for Pregnant Mothers and Their Babies

Untreated chlamydia can be passed to babies when they are born to infected mothers. This can cause8:

  • Pneumonia1
  • Conjunctivitis (eye infection)1
  • Blindness10

Another consequence of chlamydia in pregnant mothers is the risk of pre-term delivery.1 Preterm delivery can cause complications in breathing and heart and brain function in babies, and can lead to death in some cases.18

Reactive Arthritis

In rare occasions, chlamydia can cause reactive arthritis (joint disease caused from inflammation).19 Reactive arthritis can go away on its own, or may require treatment from a specialist in some cases.19

Consequences of Chlamydia in Men

For men as well as women, chlamydia can cause discomfort and mental distress from stigma attached to STIs.1 For men, long-term consequences of chlamydia infection are rare, but can be serious.1


Inflammation of the prostate gland can cause pain, burning or difficulty during urination, abdominal or pelvic pain or pain during ejaculation.20

Urethral Scarring

Chlamydia infection can lead to scarring around the urethra that blocks the pathway urine makes from the bladder to exit the body.21


Epididymitis infects the epididymis, a duct that carries sperm from the testicles. It causes inflammation, swelling and pain.22

Reactive Arthritis

As in with women, chlamydia infection in men can sometimes lead to reactive arthritis.19

Who Should Be Screened?

Because different groups of people have a higher risk of contracting chlamydia and other STIs, it is important to follow CDC guidelines for testing. Your healthcare provider will ask questions to determine if you should be tested according to recommended guidelines.

CDC Screening Recommendations23

Chlamydia Screening Recommendations
  • Sexually active women under 25 years of age.
  • Sexually active women 25 years of age and older if at increased risk.*
  • If tested positive, retesting approximately 3 months after treatment.
Pregnant Women
  • All pregnant women under 25 years of age.
  • Pregnant women, aged 25 and older if at increased risk.*
  • Retesting during the 3rd trimester for women younger than 25 years of age or at increased risk.
  • Pregnant women with chlamydial infection should have a test-of-cure 3-4 weeks after treatment and be retested within 3 months.
  • Consider screening young men in high-prevalence clinical settings or in populations with high burden of infection (MSM, etc.).
  • At least annually for sexually active MSM at sites of contact (urethra, rectum) regardless of condom use.
  • Every 3 to 6 months if at increased risk.
Persons with HIV
  • For sexually active individuals, screen at first HIV evaluation, and at least annually thereafter.
  • More frequent screening might be appropriate depending on individual risk behaviors and the local epidemiology.

Where Should I Find Out About Testing?

If you are unsure if you should be tested, there are several trustworthy resources to consider.

First, you can find out more detailed information about chlamydia and other STIs on the CDC website and on yesmeanstest.org.

Secondly, you can call your general physician, gynecologist (women) or urologist (men). Healthcare providers stay up-to-date with the latest screening recommendations. You can also speak with and make an appointment at a sexual health clinic such as Planned Parenthood.

A great opportunity for women to bring up any questions about chlamydia testing, prevention and any other specifics is during a well woman exam. The well woman exam is a yearly exam in which a healthcare provider or gynecologist carefully evaluates your sexual and overall health. During your well woman exam, your provider should suggest testing appropriate for your risk level and age group. If you are unsure if you should be tested for chlamydia, this is a great time to ask questions.

How Do I Talk to My Doctor About Chlamydia?

Your healthcare provider has a great wealth of information about STIs and testing. He or she is trained to inform you and provide a safe space for you to ask questions that may seem private or embarrassing. If you think you may have been exposed to chlamydia, are exhibiting symptoms or are in a high-risk group, make sure to let your physician know.

What if I Test Positive for Chlamydia?

If your chlamydia test comes back positive: There is a fast, painless treatment available.

Treatment for Chlamydia

Chlamydia is treated with antibiotics, which are a type of medicine that stops the growth of microorganisms (like Chlamydia trachomatis bacteria). For adults, the CDC recommends a single dose of azithromycin or a twice-daily regimen of doxycycline for 7 days.24

Regardless of which type of antibiotic you are given, you will need to abstain from sex for 7 days after your first dose of medication. If you still have symptoms following the completion of your antibiotics, continue to abstain from sex until you speak with your healthcare provider. 24

If you are a woman, you should be retested 3 months after your treatment to ensure your infection is cured and you have not become reinfected.24

Treatment for Sexual Partners

One of the most stressful parts of finding out you have chlamydia is thinking about partners you may have infected. It is very important that you tell anyone you have had sexual contact with so that they can be treated. By doing so, you can help your sex partners avoid dangerous consequences of infection, but can also avoid your chance of reinfection.24

In some cases, your healthcare provider can also prescribe medication for your sexual partner or partners. In this event, your provider will supply you with instructions for your partner to read about his or her medication. This is known as Expedited Partner Therapy (EPT). It is not available in all states. Check the CDC web page on EPT for more information.

How to Prevent Infection with Chlamydia

Whether you are trying to avoid chlamydia infection or have been tested and treated and are avoiding reinfection, there are several steps you can take to lower your risk1:

  • Abstinence from all forms of sexual contact with others
  • The use of latex male condoms during all types of sexual contact
  • Maintaining a monogamous (only 2 people) relationship with another monogamous person who has been tested for and does not have chlamydia.

The likelihood for reinfection with chlamydia is very high. Sometimes, infection persists because of improperly taken medication or antibiotic resistance. In other instances, it occurs because the treated person continues to have sex with a partner who does not receive treatment. It is very important that if you test positive, you do not have sex with your sex partner or new partners who may be infected until they have been tested and/or received treatment.25


The possibility of contracting an STI can be a scary thought. Fortunately, chlamydia and most other STIs are easy to test for and treat. It is important to remember that without treatment, serious health consequences can arise from chlamydia infection, especially in women and pregnant women. To avoid long-term consequences like infertility, patients should learn about the recommendations for STI testing and speak with their healthcare providers.

The more we learn about chlamydia, the less mysterious it becomes. At Hologic, we encourage patients to take an active role in their healthcare and know the signs and risk factors for chlamydia. The more you know about your health, the more you can continue to live healthier.


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