Chlamydia trachomatis

Comments from Expert Advisory Committee

  1. Chlamydia, caused by Chlamydia trachomatis, is the commonest STI reported in Ireland with almost half of cases diagnosed in those aged between 15 and 24 years
  2. Frequently asymptomatic in both males and females. Symptoms in males include dysuria and a urethral discharge. Symptoms in women include vaginal discharge, intermenstrual bleeding, post coital bleeding
  3. Infection can lead to epididymo-orchitis in males.
  4. Can lead to pelvic inflammatory disease (PID) in females. PID is associated with an increased risk of tubal factor infertility, ectopic pregnancy and chronic pelvic pain.
  5. Diagnosis using NAAT (nucleic acid amplification technique, e.g. PCR, polymerase chain reaction) is the current diagnostic gold standard. This is frequently combined with a gonorrhoea NAAT in the same test.
  6. Diagnosis can be made on first void urine in males and vulvovaginal or endocervical swab (less sensitive) in females1. Vulvovaginal swabs can be provider or self-taken.
  7. In sexually active men who have sex with men (MSM), three site STI testing (first void urine, pharyngeal and rectal sites ) is recommended for all, regardless of history or clinical picture. Rectal infection with invasive chlamydia types (Lymphogranuloma, LGV types2) can lead to severe proctitis presenting with rectal bleeding, pus PR, tenesmus and pain. MSM with severe proctitis symptoms should be referred promptly to GUM or ID specialist services.
  8. Test of cure is not routinely required but is recommended in rectal infection, pregnancy and in women with an intrauterine device. If doing a test of cure, wait until at least 3 weeks post completion of treatment
  9. Individuals diagnosed with chlamydia should be offered testing for other STIs including HIV, Hepatitis B, syphilis and gonorrhoea.
  10. Hepatitis C testing should be considered part of routine sexual health screening in the following circumstances: MSM, People living with HIV; Commercial sex workers; people who inject drugs (PWID). Partners of the above should also be considered for HCV testing.
  11. A diagnosis of Chlamydia in MSM should prompt a discussion about HIV prevention including PrEP.
  12. Sexual partners in the preceding 6 months should be informed of the need for testing and patients should be encouraged to inform their sexual partners. Sexual partners in the two week window period after last sexual contact may have a false negative result and should be empirically treated for chlamydia.
  13. Advise no sexual contact for 2 weeks after completion of treatment or, where indicated (see above), after negative test of cure no sooner than 3 weeks after treatment.
  14. Chlamydia is a notifiable disease. Notification process is usually initiated by the testing laboratory.

1The clinical utility of routine rectal and pharyngeal chlamydia testing is not yet established and therefore at this time it is not routinely recommended for all.

2Lymphogranuloma Venereum (LGV) is caused by an invasive serovar of Chlamydia (L1, L2, L3). L2 is the main serovar causing outbreaks in Ireland. LGV may be asymptomatic or may present with haemorrhagic proctitis, lymphadenopathy, or genital ulceration. Differential diagnosis such as herpes simplex and syphilis should be considered. There is a strong association between a diagnosis of LGV and HIV. Indications for LGV testing include MSM presenting with rectal symptoms and HIV positive MSM with confirmed rectal chlamydia. LGV testing is done on the same sample taken for chlamydia testing. Treatment is doxycycline 100mg po BD for three weeks. Patients should be referred to a sexual health service. Routine test of cure is no longer indicated if there has been full compliance with treatment and if symptoms have resolved.


Treatment of uncomplicated anogenital Chlamydia is outlined in the table below.

Azithromycin therapy should only be considered if doxycycline is contraindicated.  Doxycycline is effective in treatment of C. trachomatis infections of urogenital, rectal, and oropharyngeal sites, whereas azithromycin is less efficacious than doxycycline in the treatment of pharyngeal and rectal chlamydia.  Azithromycin therapy is also associated with macrolide resistance in Mycoplasma genitalium and high-level azithromycin resistance in gonorrhoea. If azithromycin therapy is indicated, single dose azithromycin is not recommended; a three day course is required.

Drug Dose Duration +/- Notes
1st choice option
Doxycycline 100mg every 12 hours 7 days

Contraindicated in pregnancy,

Advise to take with a glass of water and sit upright for 30 minutes after taking. Can take with food or milk if gastritis is an issue.

Advise patient to avoid excessive sunlight or artificial UV light due to risk of photosensitivity. Advise use of sunscreen/sunblock.

Absorption of doxycycline significantly impaired by antacids, iron/calcium/magnesium/zinc-containing products.
2nd choice option (If doxycycline contraindicated)
Azithromycin 1g stat followed by 500mg once a day for 2 days 3 days

Single dose Azithromycin is not recommended.

Tablets: Take with or without food.

Capsules: Take 1 hour before or 2 hours after food.


Seek specialist (GU/ID/Obs/Micro) advice in case of chlamydia in pregnant patients.

Patient Information

Safe Prescribing (visit the safe prescribing page)

Reviewed August 2022

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