## Definition and Epidemiology of Non-Gonococcal Urethritis **Key Point:** Non-gonococcal urethritis (NGU) is urethritis that occurs in the absence of Neisseria gonorrhoeae infection. Chlamydia trachomatis accounts for 30–50% of NGU cases in developed countries and is the single most common identifiable pathogen. ## Causative Organisms in NGU | Organism | Frequency in NGU | Key Features | |----------|------------------|---------------| | Chlamydia trachomatis | 30–50% | Intracellular; serovars D–K; responds to azithromycin | | Ureaplasma urealyticum | 10–15% | Lacks cell wall; variable pathogenicity | | Mycoplasma genitalium | 5–10% | Emerging pathogen; macrolide resistance increasing | | Trichomonas vaginalis | 5–10% | Protozoan; causes urethritis in men | | Other bacteria | <5% | Haemophilus, Klebsiella, Staphylococcus | **High-Yield:** In clinical practice, when a man presents with urethritis and gonorrhea is ruled out (negative Gram stain or culture), empiric therapy targets Chlamydia trachomatis with azithromycin 1 g single dose or doxycycline 100 mg BD for 7 days. ## Clinical Pearl **Clinical Pearl:** Chlamydia trachomatis is often asymptomatic in women (70–80% of infected women have no symptoms), making partner screening and treatment critical to prevent pelvic inflammatory disease (PID) and infertility. **Mnemonic:** **CHLAMYDIA causes NGU** — Remember that Chlamydia is the leading cause of NGU when gonorrhea is excluded. 
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