Overview
Chlamydia is the commonest bacterial sexually transmitted infection. WHO describes it as preventable and curable, easily treated with antibiotics, and unlikely to cause long-term problems if it is addressed early.
The difficulty is that most infections cause no symptoms at all. Left undetected in women it can spread upwards and scar the fallopian tubes, which is an important and entirely preventable cause of infertility and ectopic pregnancy.
Disease Summary
- Category
- Infectious Disease
- Cause
- Chlamydia trachomatis
- Transmission
- Sexual contact, and from mother to baby at birth
- Body System
- Urinary System
- Preventable
- Yes
- Curable
- Yes
Symptoms
Common Symptoms
Most infections cause no symptoms. Where symptoms do occur they usually begin one to three weeks after exposure.
Usually No Symptoms at All
This is the defining feature of chlamydia and the reason it spreads so widely and causes so much preventable harm.
Unusual Discharge
From the vagina or the penis. It may be thin and watery rather than thick.
Pain or Burning When Passing Urine
A common symptom in both men and women when symptoms occur at all.
Bleeding Between Periods or After Sex
A symptom in women that is easily attributed to other causes and so often missed.
Pain in the Lower Abdomen
In women this can mean the infection has spread upwards, which is when lasting damage happens.
Pain or Swelling in the Testicles
In men this indicates the infection has spread within the reproductive tract.
Anal Discharge, Pain or Bleeding
Rectal infection is usually silent but can cause these symptoms.
Red, Sticky Eyes in a Newborn
CDC states a pregnant person can pass chlamydia to the baby during childbirth, causing eye infection and pneumonia.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Lower Abdominal Pain With Fever in a Woman
This suggests pelvic inflammatory disease, where the infection has reached the womb and tubes. Prompt treatment protects fertility.
Severe Testicular Pain and Swelling
This needs same-day assessment.
Severe One-Sided Abdominal Pain in Early Pregnancy
Previous chlamydia raises the risk of a pregnancy implanting in a fallopian tube, which is life threatening and needs emergency care.
A Newborn With Red, Sticky Eyes or Breathing Difficulty
CDC states chlamydia passed at birth causes eye infection and pneumonia in babies.
Symptoms Continuing After Treatment
This needs review rather than a repeat of the same treatment.
Diagnosis
Testing Rather Than Waiting for Symptoms
Because most infections are silent, routine testing is how chlamydia is found. CDC recommends annual testing for sexually active women under 25 and for others at increased risk.
Testing in Pregnancy
WHO recommends testing during pregnancy with prompt treatment, to prevent transmission to the baby at birth.
Testing the Relevant Sites
Genital, rectal and throat sites are tested according to the person’s sexual practices, because an infection at one site says nothing about the others.
Testing for Other Infections at the Same Time
Gonorrhoea in particular occurs alongside chlamydia so often that both are tested for together as standard.
Retesting After Treatment
CDC advises retesting around three months after treatment, because reinfection from an untreated partner is common.
Laboratory Tests
Molecular Test
The standard test. It is highly accurate and can be done on a urine sample or on a swab that many people can collect themselves.
Self-Collected Swab
Many services allow people to take their own swab, which makes testing considerably easier to accept.
Gonorrhoea Test
Run on the same sample, because the two infections so often occur together and look the same.
Syphilis and HIV Tests
Offered alongside as part of a full sexual health screen.
Eye or Respiratory Swab in a Newborn
Used where a baby born to an untreated mother develops eye infection or breathing problems.
Treatment
Antibiotic Treatment
WHO states chlamydia is easily treated with antibiotics. The specific medicine and length depend on the site of infection and on national guidelines.
Treatment in Pregnancy
Different antibiotics are used in pregnancy. CDC advises a test of cure about four weeks after treatment in pregnancy.
Treating Sexual Partners
WHO states that reinfection occurs when sexual partners are not treated. Partner treatment is part of the treatment, not an optional extra.
Avoiding Sex Until Treatment Is Complete
This prevents the infection passing back and forth, which is the commonest reason it appears to return.
Retesting at Three Months
CDC advises retesting all treated people at around three months, because reinfection is common.
Prevention
Use condoms consistently and correctly
WHO names consistent and correct condom use for vaginal and anal sex as the primary prevention method.
Test regularly if you are sexually active
CDC recommends annual testing for sexually active women under 25 and for others at increased risk, because most infections cause no symptoms.
Test in pregnancy
WHO recommends testing during pregnancy with prompt treatment, which prevents eye infection and pneumonia in the newborn.
Tell partners so they can be tested and treated
WHO states that reinfection occurs when partners are not treated.
Complete treatment and avoid sex until it is finished
This is what stops the infection returning.
Retest after three months
CDC advises this because reinfection is common and equally silent.
Risk Factors
Sexually Active Young Women
CDC directs its strongest screening recommendation at this group.
- Sexually active women under 25 years
- Women 25 and older with new or multiple partners
- Women whose partner has another sexually transmitted infection
- Untreated infection in this group is the main preventable cause of tubal infertility
People With Ongoing Sexual Risk
CDC and WHO both identify groups for whom regular testing is recommended.
- People with new or multiple partners
- Men who have sex with men, tested at the relevant sites
- Sex workers and their clients
- People taking medicine to prevent HIV, who are tested regularly as part of that care
Pregnant Women and Their Babies
Untreated infection can pass to the baby during birth.
- Pregnant women under 25 and those at increased risk
- CDC advises retesting in the third trimester for those under 25 or at risk
- Babies can develop eye infection and pneumonia
- Treating the mother prevents both
Complications
Pelvic Inflammatory Disease
Spread of the infection to the womb, tubes and ovaries. It causes lasting pelvic pain and is an important preventable cause of infertility.
Infertility
Scarring of the fallopian tubes after untreated infection can prevent pregnancy. This damage is not reversed by treating the infection later.
Ectopic Pregnancy
Tubal scarring raises the risk of a pregnancy implanting in the tube, which is life threatening.
Infection Within the Male Reproductive Tract
Painful swelling of the testicle, which can affect fertility.
Eye Infection and Pneumonia in a Newborn
CDC states that a pregnant person can pass chlamydia to the baby during childbirth, causing both.
Increased HIV Risk
Untreated chlamydia makes acquiring and transmitting HIV more likely.
When to Seek Medical Care
For a Routine Test, Even Feeling Well
This is the main message of this page. Most infections are silent.
Any Unusual Discharge or Pain on Passing Urine
These deserve a test rather than a guess, because several infections cause them.
Lower Abdominal Pain With Fever in a Woman
This suggests the infection has spread and needs urgent treatment to protect fertility.
Pain or Swelling in a Testicle
This needs same-day assessment.
If a Partner Has Been Diagnosed
Go for testing and treatment even with no symptoms at all.
Prognosis
Treatment Is Simple and Effective
WHO states chlamydia is easily treated with antibiotics, usually with a single dose or a short course.
Early Treatment Prevents Long-Term Problems
WHO states chlamydia is unlikely to cause long-term problems if addressed early.
Damage From Untreated Infection Is Permanent
Tubal scarring and the infertility that follows are not reversed by later treatment.
Reinfection Is Common
Treatment gives no immunity, and CDC advises retesting at around three months for this reason.
Differential Diagnosis
Gonorrhoea
Causes an almost identical picture and frequently occurs at the same time, which is why both are tested together.
Urinary Tract Infection
Causes burning on passing urine without discharge, and is separated by a urine test.
Thrush and Bacterial Vaginosis
Cause vaginal discharge and irritation without the risk to fertility, and are separated by examination and testing.
Trichomoniasis
Another sexually transmitted infection causing discharge, separated by specific testing.
Other Causes of Pelvic Pain
Appendicitis, ovarian problems and ectopic pregnancy all need excluding where there is pain with fever.
References
World Health Organization: Chlamydia
WHO fact sheet on transmission, symptoms, complications, testing and treatment.
CDC: Chlamydia Detailed Fact Sheet
Symptoms, complications, testing, treatment and effects in pregnancy.
CDC: STI Screening Recommendations
Who should be screened for chlamydia, how often and at which sites.
World Health Organization: Sexually transmitted infections
Global estimates for chlamydia and the other curable sexually transmitted infections.
Frequently Asked Questions
Can I have chlamydia without symptoms?
Yes, and most people do. This is the defining feature of the infection and the reason it causes so much preventable harm. Only a test can tell you, which is why CDC recommends annual testing for sexually active women under 25 and for others at increased risk.
How is chlamydia treated?
With antibiotics. WHO states it is easily treated, usually with a single dose or a short course of tablets. Sexual partners need treating at the same time, because WHO states reinfection occurs when partners are not treated.
Can chlamydia cause infertility?
It can, if untreated. The infection can spread upwards and scar the fallopian tubes, which is an important preventable cause of infertility and of ectopic pregnancy. WHO states chlamydia is unlikely to cause long-term problems if addressed early.
Do I need a test if my partner was diagnosed?
Yes, even if you feel completely well. Most infections cause no symptoms, and untreated partners are the commonest reason the infection returns after treatment.
Does the test require an internal examination?
Usually not. Genital testing can be done on a urine sample, and many services offer swabs that you collect yourself. Testing is considerably easier than most people expect.