Infection:  Chlamydia trachomatis infection; Chlamydia; CT

Brief description:
  • A bacteria that causes sexually transmitted infections.
  • The commonest bacterial STI seen in the NZ population, particularly in those aged <30 years.
  • Most commonly asymptomatic. If symptomatic, typically less severe than gonorrhoea.
  • Can cause vaginal/urethral discharge, dysuria, lower abdominal pain, abnormal vaginal bleeding, testicular pain/swelling, or anal pain/discharge.
Did you know?

There are multiple different types (serovars) of Chlamydia trachomatis. Serovars A-C cause the eye infection trachoma and the L serovars cause lymphogranuloma venereum. Serovars D-K cause the typical STI discussed on this page.

Who do I test?
  • Test sexually active people aged under 30 years, and those with risk factors, including if asymptomatic.
  • Test sexually active people with signs or symptoms, and known contacts.
  • It can take up to 2 weeks to test positive if infection occurs relating to specific sexual event.
  • Positive results in people with a very low pre-test probability have a higher change of being false positives. Caution is advised when testing in very low pre-test probability groups, especially if a false positive result could have significant negative consequences e.g. children, older people in stable relationships. Many labs will not accept tests in children without prior discussion with an expert.
Test of choice:

Request Chlamydia NAAT

NAAT/PCR on vaginal swab (self- or clinician-collected) for women, first void urine (>1 hour after last void) for men. Anorectal swabs can also be taken in women based on sexual history, and is indicated in men who have sex with men, in addition to pharyngeal swabs.

  • A specific kit is usually required for NAAT testing e.g. the Aptima swabs/urine kit.
  • Gonorrhoea is tested in parallel from the same sample, and other STI testing e.g. Trichomonas can be shared also.
  • Excellent sensitivity – a negative test on a well-collected sample makes the diagnosis very unlikely
  • Excellent specificity – a positive test in an at risk person makes the diagnosis highly likely
  • First void urine can also be used in women, but is second line due to lower sensitivity. Urethral swab can also be used for men.
Other considerations:
  • All sexual contacts from the prior 3 months should be notified.
  • Reinfection is common. Offer repeat sexual health check at 3 months.
  • Test of cure is not required if symptoms resolve, unless pregnant or rectal infection.
  • Don’t retest within 4 weeks of treatment (including for test of cure), as the test may remain positive due to residual dead organisms.