Chlamydia Trachomatis (CT)

The most common bacterial STI.
Like gonorrhoea, this can also be spread vertically, and can result in aconjunctivitis in the neonate. However, unlike gonorrhoea, the conjunctivitis is not a medical emergency, and will noly very rarely result in blindness.


  • It is the most common bacterial STD
    • 10% of sexually active adults aged 15-25
    • Accounts for 40% of Non-Gonococcal urethritis in men
  • It is highly infectious – and will infect in >50% of exposures – i.e. if you have intercourse with an infected individual on only one occasion, your risk of contracting chlamydia is >50%

Clinical features

  • Urethritis (frequency and dysuria on micturition)
  • 50% of cases are asymptomatic


  • 80% of cases are asymptomatic
  • Vaginal discharge
  • Post-coital (after sex) bleeding
  • Intermenstrual bleeding
  • Lower abdominal pain
  • Infection tends to occur in the endocervical canal.


  • May acquire infection from the mother – resulting in conjunctivitis and pneumonia.


Chlamydia trachomatis is an intracellular bacteria. In many ways, its pathology is similar to that of a virus. It has a very short life-cycle. It will enter the epithelial cell, and form a reticulate body. This rapidly divides, creating hundreds of elimentary bodies. The host cell will die and release the elementary bodies,which are then able to infect more epithelial cells.


  • o  Epididymitis
  • o  Rectal infection: Proctitis
  • o  Reiter’s disease – aka Reactive Arthritis
    • Rare, as chlamydial infection usually diagnosed before it progresses this far
    • Reactive arthritis is an autoimmune reaction that occurrs in reponse to bacterial infection – usually chlamydia, and also common atfer gastroenteritis
    • Consists of the triad of:
      • Oligoarthritis – “can’t bend the knee”
      • Conjunctivitis – “can’t see”
      • Urethritis – “can’t pee”


  • Salpingitis – infection of the fallopian tubes
  • PID
    • Infertility
  • Neonatal conjunctivitis
    • Typically presents at 2-4 weeks
    • Treated with oral erythromycin (syrup)
    • Rarely causes blindness in the developed world. In Africa, a different strain is more prevalent, which is much more likely to result in blindness


Diagnosis is difficult as cell culture is difficult and expensive. Instead, indirect testing techniques are used. ELISA testing is the old method, and was unreliable. Newer methods include PCR (polymerase chain reaction) and LCR (ligase chain reaction). These methods amplify DNA constituents – to replicate fragments of DNA – which can then be identified as being chlamydial in origin (or not).
  • LCR and PCR – about 90% sensitive
    • These gene amplification tests are also sometimes referred to as NAAT (Nucleic acid amplification).
  • ELISA – about 40% sensitive


  • Men –first void (of the day) urine sample, and/or urethral swab.
  • Women – usually cervical swab, but an additional 20% of cases can be identified with urethral swab. Urine samples are notoriously inaccurate in females.
    • Taking a swab from a female – this is slightly different from the technique for gonorrhoea. Again, take a sample whilst using a speculum. There are two different swab sizes, and the larger should be used, unless the os is too small to allow passage, in which case the smaller swab (also used for male urethral sampling) may be used. The swab should go inside the cervical os, and then be rotated completely 3x.
    • Urethral swab – the disease does not normally exist only in the urethra, however, if it is present in the endocervical region, there is a chance it may also be present in the urethra.


Tetracyclines or macrolides are most useful:
  • Doxycycline – 100mg/12 hours for 7 days OR
    • This, and other tetracycline are contra-indicated in pregnancy
  • Azithromycin – 1g single dose


  • Occurs at 1wk and 3 months with:
  • Repeat smears / sampling and cultures


  • Although not an official ‘screening’ program, the NHS promotes free chlamydia and gonorrhoea testing in the R U Clear campaign.
    • Eligible to under 25’s
    • Text (SMS) details to the service, and they send out a pack in the post
    • ‘Pee in the pot’ and send it back
    • Results sent out via SMS text messaging
  • Although urethral swab (men) and endocervical swab (women) is the best way of detecting chlamydia, the urine test is deemed accurate enough in an environment of such high prevalence of STD.

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