Facts about chlamydia


Genital chlamydia is a sexually transmitted infection caused by the Chlamydia trachomatis bacterium. Sexually active young people are most at risk of chlamydia, and women below 24 years of age have the highest number of infections in Europe.

The EU and EEA/EFTA countries are expected to report genital chlamydia infections to ECDC. Chlamydia disease surveillance shows that the number of Chlamydia infections is increasing in Europe:  there are now more than 250 000 new cases reported each year. Many Chlamydia infections do not produce symptoms, and the growing number of reported cases is likely to be the result of increased awareness about the disease and intensified testing.

Chlamydia trachomatis infections can cause long-term complications in women even when they do not produce symptoms of acute disease. The most common complications are pelvic inflammatory disease (PID) and salpingitis, conditions that can lead to infertility and extra-uterine pregnancies. This risk of long-term reproductive health problems associated with C. trachomatis infections has lead some European countries to routinely offer testing for chlamydia to sexually active young people in an attempt to reduce the spread of the disease


Chlamydia infections (genital)

Genital chlamydia is the leading sexually transmitted infection in Europe and the cause of considerable acute morbidity and long term reproductive health problems, particularly in young people. Many infections are asymptomatic resulting in delayed diagnosis and uninterrupted transmission. Chlamydia salpingitis can cause tubal adhesions and is an important risk factor for female infertility and extra-uterine pregnancy. It is an important cause of pelvic inflammatory disease. Chlamydia is under epidemiological surveillance within the EU. The reported national incidence rates vary widely and most of the more than 250 000 cases reported to ECDC for 2007 were notified by only five countries.  The number of reported cases reflects the intensity of testing rather than true differences in disease burden.

The pathogen

  • Genital chlamydia is caused by the obligate intracellular Gram negative bacterium Chlamydia trachomatis
  • Chlamydia trachomatis is one of four species in the genus Chlamydia and the family Chlamydiaceae which also include C. pneumoniae, C. psittaci and C. pecorum.
  • Chlamydia trachomatis causes acute eye infections, trachoma, genital infections and the more invasive sexually transmitted infection; lymphogranuloma venereum (LGV). 
  • The strains that cause eye and genital infections are labelled D through K and grow only in the columnar and squamo-columnar epithelial cells that make up the conjunctivae and the mucosa in the respiratory tract, urethra, cervix and rectum. 
  • Lymphogranuloma venereum is caused by the invasive L1, L2 and L3 strains of C. trachomatis, sometimes referred to as the LGV serovars.

Clinical features and sequelae

  • Genital infections with C. trachomatis present as urethritis and proctitis in men and women, cervicitis, salpingitis, endometritis and pelvic inflammatory disease (PID) in women, and orchitis, epididymitis and prostatitis in men. 
  • Perinatal transmission of C. trachomatis can result in conjunctivitis (ophthalmia neonatorum) and pneumonia in newborns and young infants.
  • Conjunctivitis and respiratory infections can be the result of contact with contaminated hands, or direct exposure to semen and vaginal fluids. 
  • At least 70% of genital C. trachomatis infections in women and 50% in men are asymptomatic at the time of diagnosis.
  • The natural course of genital chlamydia infections is not well understood:
    • Spontaneous resolution of asymptomatic infections is not uncommon.
    • Asymptomatic infections, particularly endocervical infections, can persist for long periods. 
    • Many patients with asymptomatic infections will at some point develop symptoms and clinical disease.
    • Asymptomatic infections can result in complications such as blocked tubes and pelvic inflammatory disease.
  • Lymphogranuloma venereum (LGV) affects both men and women.


  • Symptoms include urgency, frequency, burning sensation and pain when passing urine in both men and women. 
  • Dysuria in women often reflects concurrent urethral and endocervical infections.  
  • Acute urethral syndrome is a condition with symptoms suggestive of lower urinary tract infection in the absence of significant bacteruria (< 105 organisms/ ml of urine) that can be caused by C. trachomatis.
  • In men, genital chlamydia typically presents as dysuria and urethral discharge. The discharge tends to be less profuse than that produced by gonococcal infections, but there is significant overlap between the two diseases and chlamydia cannot be distinguished clinically from gonorrhoea or other causes of urethritis.
  • Only about half of genital C. trachomatis infections in men are symptomatic. In one study in which infected men were observed without treatment for a minimum of 21 days, one in eight developed symptomatic urethritis.
  • Some 30% to 50% of non-gonococcal urethritis is believed to be due to C. trachomatis.


  • Endocervical chlamydia infections present as vaginal discharge, bleeding between periods, mild abdominal pain, and often dysuria.
  • Seven out of ten women with endocervical infection have no or only mild symptoms that may not prompt medical contact. 
  • About half of all genital chlamydia infections in women are concurrent urethral and cervical infections.


  • Salpingitis is typically the result of an ascending lower reproductive tract infection and can be symptomatic or without clinical signs and symptoms.
  • Symptoms include fever, discomfort and pain in the lower abdomen, and tenderness on palpation.


  • Proctitis manifests as anal pruritis and rectal discharge. The infection is limited to the rectum and resembles gonococcal proctitis. 
  • Asymptomatic rectal infections are common. 
  • C. trachomatis is a common cause of proctitis in men who have sex with men. Proctitis can result from direct inoculation of the rectum in both men and women through anal intercourse, or through secondary spread of secretions from the cervix.

Lymphogranuloma venereum (LGV)

  • The classical disease presents in three stages:
    • In the first stage a transient ulcer forms on the external genitalia at the site of inoculation; this stage often passes unnoticed. In rectal infections, the first manifestation can be acute proctitis. 
    • Most patients present in the second stage, when the involved regional lymph nodes become firm, swollen and painful. Fever and malaise commonly accompany local symptoms. The primary genital ulcer often resolves before or during this stage, but proctitis is likely to persist.
    • The third stage is due to the lymphatic damage and is characterised by lymphoedema and sometimes secondary ulceration. Scarring, strictures and fistulae involving the inguinal glands, genitalia, anus and rectum may develop.
  • The clinical presentation of LGV proctitis is often different from the classical disease. Common symptoms include haemorrhagic purulent rectal discharge and constipation and patients usually do not have symptoms of urethritis or swollen inguinal lymph nodes.


  • Nucleic acid amplification tests (NAAT) are the most sensitive (90-95%) and the most widely used tests for genital chlamydia. They detect all serovars of C. trachomatis including the LGV serovars. An advantage of NAATs is that they can detect C. trachomatis in first void urine and self-administered vulvovaginal swabs in addition to urethral, cervical and rectal swabs which makes them suitable for large volume screening. Commonly used NAATs techniques include:
    • Polymerase Chain Reaction (PCR)
    • Ligase Chain Reaction (LCR)
    • Strand Displacement Amplification (SDA)
    • Transcription-mediated Amplification (TMA)
  • Direct Fluorescent Antibody tests (DFA) can be used on all specimens but have low sensitivity and are comparatively labour intensive.
  • Enzyme-linked Immunosorbent Assay tests (EIA) can be used on all specimens. They are inexpensive compared but are less sensitive than NAATs.
  • Point of Care Tests (POTs) allow treatment of the patient while in the clinic but are expensive and not suitable for large volume testing in the clinical setting. Sensitivity is less than for NAATs. POTs can be used for self-collected vaginal swabs and allows for self-testing outside of the clinic.
  • Cell-culture can be used on all specimens and allows for susceptibility testing. It is a highly specific method but has low sensitivity (60-80%), and is comparatively more expensive and technically more difficult than non-culture tests.
  • Chlamydia serology can be used for diagnosing chronic infections and for estimating life-time infection but does not add to the clinical management of acute infections or the screening of asymptomatic patients. High titers of immunoglobulin G (IgG) antibodies are common in pelvic infections.
  • The case definition for genital chlamydia infection for the purpose of reporting to the community network is available  here.

Sequelae and complications

  • A common complication of genital chlamydia in women is pelvic inflammatory disease, which includes any combination of endometritis, salpingitis, tuboovarian abscess and pelvic peritonitis. PID can result in ectopic pregnancy, infertility and chronic pelvic pain. 
  • Chlamydia is responsible for 50% of the cases of PID and between 10% and 30% of women with genital chlamydia infections develop PID. 
  • Serological studies of women with tubal infertility indicate that chlamydia infection may be the cause of the adhesions in more than half of the cases. 
  • It is estimated that tubal adhesions as a consequence of chlamydia salpingitis are responsible for about 40% of ectopic pregnancies. 
  • Ectopic pregnancy occurs in about 1% of all pregnancies and it is the commonest cause of maternal death in the first trimester. 
  • Perinatal transmission can cause  ophtalmia neonatorum and pneumonitis in newborns.
  • Chlamydia infections can cause reactive arthritis, Reiter’s syndrome, and adult conjunctivitis. 
  • There is some evidence that genital chlamydia infection may contribute to miscarriage, premature rupture of membrane, preterm birth, still birth and low birth weight. 


  • Genital chlamydia infection is a disease of sexually active young people. The infection rates are highest in females below 20 years of age and decrease with increasing age.
  • Two-thirds of all infections are in people aged 15-24 years.
  • In 2007, the incidence in the 15 – 24 years age group was more than four and a half times that in the 25 – 44 years age group.
  • The reported incidence of genital chlamydia has increased dramatically in Europe over that last 20 years. It is not established to what degree the increase is due to increased testing rather than a true increase in the incidence of chlamydia. 
  • The risk factors for chlamydia infection are general and include:
    • Young age ( < 24 years),
    • New sexual partner,
    • Multiple sexual partners (more than one sexual partner in the past one year), and
    • Inconsistent or non-use of condoms.
  • Sexual risk behaviour is an important risk factor and reinfection rates of 10-30% have been documented in young adolescents with multiple sex partners.
  • The male to female ratio for notified cases in 2007 was 1:1.2 for all ages and 1:1.6 in the 15-24 years age group. The skewed sex ratio is largely explained by the fact that young women have more testing opportunities than young men.
  • Chlamydia infection rates above 10% have been found in young women attending STI clinics. Population-based studies among under 30-year-old women have found prevalence rates of between 2 and 6% in the Netherlands, Denmark and the UK.
  • Classical lymphogranuloma venereum is relatively rare in Europe associated with unprotected sexual contacts outside of Europe including South-East Asia, South America, Africa and the Caribbean.
  • In 2003-2004 an outbreak of LGV proctitis was detected in the Netherlands among men who have sex with men (MSM).  Since then, increasing number of cases has been reported from several European countries. The disease is confined to the (MSM) population and a large proportion of affected patients have concomitant HIV infection.


  • Chlamydia infection is predominantly transmitted through sexual intercourse but may also be transmitted from mother to a newborn child during delivery. 
  • The incubation from infection to first symptoms is one to three weeks.


  • No vaccine is available against C. trachomatis
  • Consistent condom use outside of monogamous relationships is the most effective primary prevention.
  • Chlamydia control relies on effective secondary prevention and include:
    • Easy access to counselling and testing for symptomatic sexually transmitted infections.
    • Opportunistic testing and screening of sexually active young people.
    • Effective partner management of diagnosed cases.
  • Partner management aims to contact, counsel and test all sexual contacts of the index case in order to break the chain of transmission. Approaches to partner management range from provider notification and referral to the index patient being responsible for notifying sexual partners. 
  • It has been shown that active screening for genital chlamydia infection can reduce the incidence of PID.

Management and treatment

  • Chlamydia is effectively treated with antibiotics and doxycycline and azithromycin typically have cure rates of 95% for uncomplicated chlamydia. 
  • Control of infection is centred on case management, partner treatment, health promotion activities and the use of barriers such as condoms.
  • Pregnant patients with uncomplicated chlamydia can be treated with amoxicillin or erythromycin.

Note: The information contained in this fact sheet is intended for the purpose of general information and should not be used as a substitute for the individual expertise and judgement of healthcare professionals.



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