Chlamydia is a common sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. An estimated 2.86 million infections occur annually in the United States. Chlamydia is known as a “silent” infection because the majority of infected people have no symptoms. For this reason, chlamydia often goes undiagnosed and can lead to serious health problems in both women and men if left untreated.
What is chlamydia?
Chlamydia is caused by the bacterium Chlamydia trachomatis. There are multiple strains or serovars of C. trachomatis that affect humans. Serovars D-K primarily cause genital tract infections. The bacteria are spread through unprotected vaginal, anal, or oral sex with an infected partner. Chlamydia can also be passed from an untreated mother to her baby during childbirth.
How common is chlamydia?
Chlamydia is extremely common, especially among young people. In the United States:
- Over 1.7 million cases were reported to the CDC in 2017, though an estimated 2.86 million infections occur annually.
- It is the most frequently reported bacterial STI in the country.
- Prevalence is highest among sexually active girls and young women ages 15-24 years old.
- An estimated 1 in 20 sexually active young women aged 14-24 years has chlamydia.
Rates of infection have been increasing steadily over the past 30 years, likely due to increased screening and improved diagnostic tests. However, the true burden of infection is underestimated since most cases are asymptomatic and not diagnosed.
Signs and symptoms
Women
Up to 80% of women with chlamydia have no signs or symptoms. When symptoms do occur, they may include:
- Abnormal vaginal discharge that may be clear, cloudy or yellow
- Burning/itching around the vagina
- Burning during urination
- Bleeding during or after sex
- Lower abdominal pain
- Fever
- Nausea
- Pain during sexual intercourse
Men
Up to 50% of men have no symptoms. When present, signs and symptoms may include:
- Clear or cloudy discharge from the penis
- Burning/itching around the opening of the penis
- Burning during urination
- Pain and swelling around the testicles
Why is it called “silent”?
Chlamydia is known as a “silent” STI because the majority of infected men and women have no symptoms and are unaware they are infected. Even when signs and symptoms do occur, they are often mild and not easily recognized as an STI. As a result, many infections go undiagnosed and untreated.
The bacteria’s ability to cause silent infections, combined with high transmission rates, enables chlamydia to spread rapidly among sexually active individuals. Globally, chlamydia is the most common bacterial STI.
Health risks of untreated chlamydia
When left untreated, chlamydia can lead to serious reproductive health complications.
In women
Up to 40% of women with untreated chlamydia develop pelvic inflammatory disease (PID), an infection of the uterus and fallopian tubes. PID can cause:
- Infertility
- Chronic pelvic pain
- Ectopic pregnancy (pregnancy outside the womb)
- Abscess formation
Women with untreated chlamydia are up to 5 times more likely to become infected with HIV, if exposed.
In men
Complications are rare, but untreated chlamydia may lead to:
- Epididymitis, an infection of the epididymis (tubes carrying sperm)
- Urethritis, infection of the urethra
- Proctitis (rectal inflammation) in men who have anal sex
Rarely, it may cause reduced fertility.
In babies
Babies born to infected mothers can get chlamydia in their eyes and respiratory tracts. This can lead to pneumonia or conjunctivitis that develops within 3 weeks after birth.
Who should be tested?
Because chlamydia is so prevalent and most infections are asymptomatic, the CDC recommends regular screening for people at increased risk:
- All sexually active women under age 25
- Women over 25 with risk factors like new or multiple sex partners
- Any women with HIV
- Sexually active gay and bisexual men
- Anyone with an infected partner
Pregnant women should be tested again in the third trimester to prevent transmitting the infection to their baby.
How is it diagnosed?
There are several options for diagnosing chlamydia:
Nucleic acid amplification tests (NAATs)
NAATs detect the genetic material (DNA) of C. trachomatis. These are the most sensitive tests available. Samples can be obtained from:
- Urine
- Vaginal swab
- Endocervical swab
- Urethral swab in men
Results take 1-3 days and may remain positive for 3-5 weeks after treatment.
Cell culture
Chlamydia bacteria can be grown and identified in cell cultures from cervical, urethral, or urine samples. This test is relatively slow and less sensitive than NAATs.
Direct fluorescent antibody test
This rapid test uses fluorescent-tagged antibodies to detect chlamydia antigens in samples from the cervix or urethra. It is less sensitive than culture or NAATs.
DNA probe test
This test uses DNA probes to bind to genetic material of chlamydia bacteria, confirming their presence. It is relatively fast but less sensitive than other methods.
How is chlamydia treated?
Chlamydia is easily cured with antibiotic treatment. The CDC recommends:
- Azithromycin (single 1g oral dose) OR
- Doxycycline (100mg twice per day for 7 days)
No vaccine is currently available. Patients should abstain from sex for 7 days after starting antibiotics and until all partners have been treated. Test of cure is not routinely recommended if treatment is completed.
All recent partners should be notified, tested, and treated to avoid reinfection. Regular screening is essential since repeat infection is common.
Using condoms correctly every time you have sex can reduce the risk of getting or spreading chlamydia.
Prevention
Because chlamydia has few symptoms, spreads easily, and can lead to lasting complications, prevention is essential. Recommendations include:
- Get screened at least once a year if sexually active and under 25.
- Use condoms correctly every time you have sex.
- Limit your number of sex partners.
- Talk to your partner(s) about STIs and getting tested.
- Don’t have sex with someone who has symptoms or a positive test that has not been treated.
- Take antibiotics properly and finish all medication.
- Return for follow up testing if advised by your doctor.
Regular chlamydia screening is especially important for young women to preserve reproductive health. Pregnant women should be screened to prevent transmission to infants.
Conclusion
Chlamydia is extremely common but most infected people have no symptoms, allowing it to spread undetected. All sexually active women under 25 should get annual screening, even if they feel healthy.
Left untreated, chlamydia can seriously impact a woman’s fertility. It can also increase susceptibility to other STIs like HIV. Condoms and limiting sex partners helps reduce risk.
With early detection and antibiotic treatment, complications can be avoided. Don’t assume you’re STI-free or that a partner’s history is safe – get tested regularly. Talk to partners about testing before having sex.