Is Nongonococcal Urethritis (NGU) an STI? What to Know

Nongonococcal urethritis (NGU) is the inflammation of the urethra (the tube through which urine exits the body) caused by something other than gonorrhea.

By far, the most common cause is chlamydia. Although other bacteria, viruses, fungi, and parasites can also cause urethral inflammation, NGU is transmitted almost exclusively through vaginal, anal, and oral sex.

NGU is more common in males than females, causing symptoms like itching, pain when urinating, and a discharge from the penis. In females, there may be no symptoms until complications like pelvic inflammatory disease (PID) develop. The treatment of NGU depends on the underlying cause.

This article explains the causes and symptoms of nongonococcal urethritis, including how the condition is diagnosed, treated, and prevented.

A person consulting with a healthcare provider

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Gender Definitions

For purposes of this article, "male" and "man" refer to a person with a penis, and "female" or "woman" refer to a person with a vagina, regardless of the gender or genders they identify with. When research or health authorities are cited, the gender terms reflect those used in the cited source.

What Causes Nongonococcal Urethritis?

NGU is strongly associated with treatable sexually transmitted infections (STIs). In males, anywhere from 20% to 50% of cases are caused by chlamydia (Chlamydia trachomatis), while 10% to 30% are caused by Mycoplasma genitalium (M. genitalium or Mgen).

Other viruses, bacteria, fungi, and parasites are also known to cause NGU, albeit less commonly. Although some of these causes (like Escherichia coli and yeast infection) are not regarded as STIs, sexual transmission is seen to be the primary route of infection to the urethra.

Causes of NGU
Bacterial   Viral Fungal Parasitic
Chlamydia Herpes simplex virus type 1 (HSV-1) Candida albicans (yeast infection) Trichomonas vaginalis
Mycobacterium genitalium  (M. genitalium) Herpes simplex virus type 2 (HSV-2)  
Escherichia coli (E. coli) Adenovirus  
Bacterial vaginosis (BV) Epstein-Barr virus (EBV)
Mycobacterium hominus
Neisseria meningitidis
Haemophilus vaginalis
Gardnerellla vaginalis  
Ureaplasma urealyticum  
Ureaplasma parvum  

There are also nonsexual causes of NGU, including urinary tract infections (UTIs), bacterial prostatitis (infection of the prostate), urethral stricture (narrowing of the urethra), phimosis (a foreskin that cannot retract), urinary catheters, and irritants (like spermicides).

But these are less likely culprits, and some NGU cases are entirely idiopathic (meaning of unknown origin).

Gonococcal Urethritis vs. Nongonococcal Urethritis

Gonococcal urethritis is caused by the bacterium Neisseria gonorrhoeae, which is also called gonococcus. Nongonococcal urethritis is urethritis caused by everything other than gonorrhea. For this reason, NGU is sometimes called nonspecific urethritis (NSU).

Urethritis is most often caused by an STI. By far, the two most common are gonorrhea and chlamydia. Both are gram-negative bacteria with very different physical characteristics.

If a person has symptoms of urethritis, a swab will be taken from the urethra and examined under the microscope. If gonorrhea is ruled out, NGU is diagnosed.

With that said, it is not uncommon for a person to have gonorrhea, chlamydia, and even M. genitalium all at the same time.

Who Gets NGU?

NGU is more common in males, but people of any sex can acquire it.

Males are vulnerable to NGU due to the makeup of their urethra. Compared to the female urethra, which is rich in mucus and microorganisms that shield it from infection, the male urethra has less mucus and relatively few protective microorganisms.

Vaginal sex also appears to change the composition of microorganisms in the male urethra, making cells and tissues more vulnerable to STIs like chlamydia.

Meanwhile, anal sex exposes the male urethra to enteric (intestinal) bacteria like E. coli found in feces. There are few ways to get an E. coli infection in the urethra other than through sex.

While females can get NGU from an STI like chlamydia, the majority of cases will be asymptomatic, meaning without symptoms. If there are symptoms, they are more likely to involve the cervix, rectum, or throat.

By comparison, males with NGU are 3 times more likely to have symptoms than not. Symptoms typically involve the urethra, rectum, or throat.

How Does NGU Spread?

The infectious agents that cause NGU can be transmitted (passed) through vaginal (penis-to-vagina) and anal (penis-to-rectum) sex. Several infections are also readily spread through oral (penis-to-throat) sex, including M. genitalium, herpes simplex virus types 1 and 2, and Haemophilus strains.

Factors that increase the odds of transmission include:

  • Being a young male between the ages of 15 and 30
  • Having multiple sex partners (increasing the risk by 20% for each additional partner)
  • Not using condoms
  • Not using lubricants
  • Having had chlamydia in the past

NGU Symptoms

The symptoms of nongonococcal urethritis can vary based not only on the type of infection you have but also on whether you have a penis or vagina.

Common symptoms of NGU include:

  • Pain or burning with urination (dysuria)
  • A clear or creamy urethral discharge (typically light)
  • Urethral itching (pruritus)
  • Stained underwear

Males might also experience inflammation of the penis head (balanitis), foreskin (posthitis), and opening of the penis (meatitis).

Females often experience the need to urinate urgently or frequently. There may also have vaginal pain, discharge, and bleeding due to cervicitis (inflammation of the cervix), a condition that often accompanies NGU in females.

Can You Tell NGU From Gonorrhea?

With NGU, the urethral discharge will usually be thin, clear or creamy, and relatively sparse. By contrast, the urethral discharge from gonorrhea is usually copious, thick, and pus-like.

How Long Can You Spread NGU?

The STIs that cause NGU can be transmitted from the time the infection occurs until the infection is treated and cured. This poses significant health concerns as many people with chlamydia and M. genitalium are asymptomatic and may unwittingly transmit it to others without even realizing it.

Untreated chlamydia may spontaneously clear without treatment in roughly 1 in 5 people, but there is no way to predict in whom the infection might persist or clear. M. genitalium can also clear, usually within one year, but only testing can tell when you are no longer likely to transmit it.

Because of this, you should never wait for chlamydia or M. genitalium to go away on its own. Left untreated, they can cause serious harm to your health and the health of others.

Testing for NGU

An NGU diagnosis is made when a person with urethritis is tested and gonorrhea is ruled out as a cause.

The diagnosis starts with a review of your symptoms and medical history. This may include questions about your sex life and sex partners. A physical exam is then performed to examine your urethra.

To confirm whether gonorrhea or some other agent is involved, your healthcare provider will take a swab of urethral discharge to examine under the microscope. The sample is then smeared onto a glass slide and dyed with a Gram stain.

The Gram stain can determine if there are any gram-negative bacteria in the sample and if they have the telltale features of Neisseria gonorrhoeae (namely, a round shape connected in pairs like a peanut). If they do not, NGU is diagnosed.

How Accurate Is Gram Staining?

A 2018 study in the First International Journal of Andrology reported that Gram staining of urethral smears have a 92.9% sensitivity in correctly detecting gonorrhea.

Thereafter, a NAAT (nucleic acid amplification test) can be performed on a swab or urine sample to determine if chlamydia or M. genitalium is involved. The NAAT does so by detecting the genetic material of the bacteria.

Other tests may be ordered to investigate other possible causes.

NGU Treatment

As the predominant causes of NGU, chlamydia and M. genitalium are both treated with oral antibiotics to clear the infection.

While the choice of antibiotic will ideally be matched to the type and strain of bacteria you have, this is not always possible. In such cases, the Centers for Disease Control and Prevention (CDC) recommends that the following antibiotics be prescribed presumptively (based on the probability of an infection):

  • Doxycycline 100 milligrams (mg) taken by mouth twice daily for seven days (preferred option)
  • Zithromax (azithromycin) 1 gram (g) taken by mouth in a single dose
  • Zithromax (azithromycin) 500 mg taken in a single dose, followed by 250 mg taken by mouth once daily for four days

The antibiotics can treat both infections, but doxycycline generally has greater activity against Chlamydia trachomatis, while Zithromax tends to have greater activity against M. genitalium.

Antibiotics may also be prescribed presumptively if the cause is unknown. Other medications still may be prescribed if a viral, fungal, or parasitic cause is diagnosed.

What Happens If I Don’t Get Treated?

Leaving any STI untreated places sexual partners at risk of infection. But it also places your own health at risk.

Untreated, chlamydia can lead to potentially serious complications in people of any sex, including:

If I Have Had an NGU Infection, Am I Immune?

Getting treated and cured of an STI doesn't mean you can't get it again. In fact, studies suggest that 1 in 7 females aged 14 to 34 in the United States will get reinfected with chlamydia within four months of being successfully treated.

One problem with reinfection is that repeated exposure to antibiotics increases the risk of antibiotic resistance, causing the drugs to become less and less effective.

In recent years, increasing rates of resistance have been seen with Zithromax, a drug used to treat a host of infections. Because of this, the CDC recommends multiple-day treatment with Zithromax—rather than a single dose—for certain people, including those with a history of STIs.

With most STIs, exposure does not make you immune to the infections. So you can get them again and again unless you take steps to change behaviors and reduce your risk of exposure.

How to Prevent the Spread of NGU

With NGU, the main route of infection is sexual, so it's important to practice safer sex and improve sexual hygiene to reduce your risk of infection.

You can do so in the following ways:

  • Limit your number of sex partners.
  • Use condoms consistently and correctly.
  • Wash your genitals with soap and water after sex, particularly after anal sex.
  • Avoid sex if you think you've been exposed, and visit a healthcare provider or local STI clinic.
  • Notify all sexual contacts if you've been diagnosed with an STI so they can get tested and treated as well.

Chlamydia Screening Recommendation

Because chlamydia in women is often asymptomatic, the CDC recommends annual screening for all sexually active women under 25 years and for women 25 years or older who are at increased risk of infection. Annual chlamydia screening is also advised for all sexually active men who have sex with men.

Summary

Nongonococcal urethritis (NGU) is inflammation of the urethra not caused by gonorrhea. NGU is mainly sexually transmitted. Chlamydia and Mycobacterium genitalium account for the lion's share of NGU diagnoses.

Males get NGU more often than females due to anatomical differences in the urethra of males vs. females. Symptoms include pain with urination, itching, and a clear or creamy discharge. If left untreated, NGU can lead to pelvic inflammatory disease, chronic prostatitis, reactive arthritis, and pregnancy complications.

NGU can be diagnosed by taking a swab of the discharge and viewing it under the microscope with special stains. NGU is typically treated with oral antibiotics. Other drugs may be needed if the cause is viral, fungal, or parasitic.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By James Myhre & Dennis Sifris, MD
Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator.