What Causes NGU and How It's Treated

What is nongonococcal urethritis?

Nongonococcal urethritis, or NGU, is inflammation of the urethra, the tube that carries urine out of the body, that is not caused by gonorrhea. It is a description of a symptom pattern — burning with urination and discharge — rather than a single disease, which is why the phrase 'nongonococcal urethritis' is really shorthand for 'urethritis, cause still being worked out.'

The diagnosis is usually made on clinical grounds first: discharge, burning with urination, or urethral discomfort, sometimes confirmed with a swab showing inflammation before any specific organism is identified. A negative gonorrhea test is what actually earns the 'nongonococcal' label — it says one common cause has been ruled out, not that the remaining possibilities have been narrowed down to just one.

Nongonococcal urethritis explained covers the broader picture of this diagnosis in men; this article focuses specifically on what causes it and how the treatment approach is actually chosen, since NGU is defined by what it is not — gonorrhea — more clearly than by what it is.

What actually causes NGU

Chlamydia is the single most identifiable cause of NGU, a common and curable bacterial infection that is frequently silent even as it inflames the urethra 1Ref 1Centers for Disease Control and Prevention (2024).About Chlamydia.Supports that chlamydia is a common, curable bacterial STI that is frequently asymptomatic and can cause pelvic inflammatory disease if untreated, used here as the leading identifiable cause of NGU.. After chlamydia, Mycoplasma genitalium is the next most common identified cause, though it is not part of a routine urethritis workup and is usually only tested for when symptoms persist after standard treatment 2Ref 2Centers for Disease Control and Prevention (2021).Mycoplasma genitalium - STI Treatment Guidelines.Supports that M. genitalium testing is not recommended for an initial urethritis workup but is considered for persistent symptoms after empiric treatment, and describes the treatment approach based on macrolide resistance..

Trichomoniasis, a curable infection caused by a parasite rather than a bacterium, is another possible cause, and it is unusual among urethritis causes in that most people who have it, of either sex, have no symptoms at all 3Ref 3Centers for Disease Control and Prevention (2024).About Trichomoniasis.Supports that trichomoniasis is a common curable STI caused by a parasite, that the majority of infected people have no symptoms, and that it is treated with oral antibiotics, used here as one identified cause of NGU.. Genital herpes can cause urethritis as well, particularly during a first outbreak, and less commonly an adenovirus or a bacterium unrelated to sexual contact is responsible. In a meaningful share of cases — often a third or more in clinical series — no cause is ever identified on standard testing, which is its own recognized category rather than a testing failure.

Why the first round of treatment doesn't wait for every test result

Because chlamydia is the most common and most consequential cause to miss, clinicians typically start antibiotic treatment for the most likely causes as soon as urethritis is confirmed, rather than waiting days for every test result to return. This is standard practice precisely because delaying treatment for a likely chlamydia infection carries real downsides, including ongoing transmission to partners and, in women who may be exposed by an infected partner, a higher chance of pelvic inflammatory disease.

The comprehensive national treatment guideline that covers chlamydia, gonorrhea, trichomoniasis, and other causes of urethritis is what shapes this sequencing: treat for the likely causes now, then revisit the diagnosis if the response is incomplete 4Ref 4Workowski KA, Bachmann LH, Chan PA, et al. (Centers for Disease Control and Prevention) (2021).Sexually Transmitted Infections Treatment Guidelines, 2021.The comprehensive U.S. evidence-based diagnostic and treatment recommendations covering chlamydia, gonorrhea, trichomoniasis, and other causes of urethritis, used here as the source of record for treating the most likely causes before full lab confirmation.. That is different from treating blindly — it reflects which causes are common enough, and serious enough if missed, to act on before lab confirmation.

When symptoms don't clear after treatment

Persistent or recurrent urethritis after a first round of treatment is common enough that it has its own name — persistent or recurrent NGU — and its own next steps, rather than being treated as a treatment failure to repeat with the same antibiotic. At this point, Mycoplasma genitalium testing becomes relevant, since it is specifically reserved for situations exactly like this one 2Ref 2Centers for Disease Control and Prevention (2021).Mycoplasma genitalium - STI Treatment Guidelines.Supports that M. genitalium testing is not recommended for an initial urethritis workup but is considered for persistent symptoms after empiric treatment, and describes the treatment approach based on macrolide resistance., and a clinician may also reconsider whether the original treatment was taken as directed, whether a partner was treated, or whether reinfection from an untreated partner explains the return of symptoms.

Mycoplasma genitalium treatment, once identified, differs depending on whether the specific strain resists the first-choice antibiotic, which is one reason persistent NGU sometimes takes more than one visit to resolve. This is a sequence built around ruling causes in and out, not a sign that urethritis is unusually hard to treat once the actual cause is known.

A smaller group of people go through this entire sequence — chlamydia treatment, then Mycoplasma genitalium testing and treatment — and still have no organism identified despite persistent symptoms. At that point a clinician typically looks beyond infection entirely, considering irritation, a structural issue, or a different inflammatory process, rather than continuing to cycle through antibiotics without a clearer target.

Partners and reinfection

Any recent sex partner is worth having evaluated and treated alongside the person with symptoms, since several NGU causes, chlamydia most of all, are easily passed back and forth between partners who are not treated at the same time. Reinfection from an untreated partner is one of the most common reasons NGU symptoms return after treatment that otherwise worked.

For chlamydia specifically, expedited partner therapy allows a clinician to provide treatment for a partner who is unlikely to seek care on their own, without that partner needing a separate visit first 5Ref 5Centers for Disease Control and Prevention (2021).Expedited Partner Therapy.Defines expedited partner therapy and supports that providers should routinely offer it for chlamydia when a patient's partner is unlikely to seek timely treatment on their own.. Whether this option is available depends on state law and the specific infection involved, so it is worth asking about directly rather than assuming it does or does not apply.

Getting tested and treated confidentially as a minor

Every state and Washington, D.C. allow minors to consent to their own STI testing and treatment without a parent's involvement, though the specific minimum age and the rules around whether a parent can be notified vary by state 6Ref 6Guttmacher Institute (2024).Minors' Access to STI Services.Supports that all 50 states and DC allow minors to consent to STI testing and treatment, with a subset permitting but not requiring parental notification.. This matters for NGU specifically because delaying evaluation out of concern about parental notification allows an underlying infection like chlamydia more time to cause complications.

Can a minor consent to sti treatment covers this in more depth for anyone weighing whether to seek care independently. A title X-funded clinic, a school-based health center, or a sexual health clinic are generally reliable places to ask directly about confidentiality policies before an appointment.