Aetiology

The aetiology of urethritis can be divided into infectious or non-infectious causes.

Infectious urethritis is further divided into:

• gonococcal urethritis
  • “classic” form of infective urethritis
  • caused by Neisseria gonorrhoeae (1)
• non-gonococcal urethritis (NGU)
  • most often caused by either Chlamydia trachomatis or Mycoplasma genitalium
  • the two organisms are more likely to be detected in
    • younger patients with NGU, although this association is not as strong for M genitalium
    • those with a urethral discharge and/or dysuria
    • C. trachomatis and M. genitalium may be less common in men who have sex with men (MSM) than heterosexual men with NGU
    • M. genitalium has been associated with balano-posthitis and C. trachomatis with a circinate balanitis
  • both organisms infrequently coexist in the same individual with NGU, but dual infections have been identified in up to 10% of men in some studies (2)
  • less common – Trichomonas vaginalis, Gardnerella vaginalis, Ureaplasma urealyticum, herpes simplex virus (HSV), adenovirus (1)

In persistent/recurrent urethritis, aetiology is most likely to be multifactorial

• an infectious agent is identified in less than 50% of cases
• Mycoplasma genitalium is identified in 20–40%
• C. trachomatis is reported in 10%–20% of men treated with azithromycin 1g
• additionaly, U. urealyticum and T. vaginalis have also been implicated

Note:

• the term nonspecific urethritis (NSU) should be not be used since it applies to nongonococcal, non-chlamydial urethritis and may result in confusion (1)

Reference:

1. Centers for Disease Control and Prevention. Sexually transmitted infections treatment guidelines, 2021. Jul 2021 [internet publication]
2. Jordan SJ, Toh E, Williams JA, et al. Aetiology and prevalence of mixed-infections and mono-infections in non-gonococcal urethritis in men: a case-control study. Sex Transm Infect. 2020 Jun;96(4):306-11.