Overview of Nongonococcal Urethritis

Nongonococcal urethritis, or NGU, is defined as any form of urethritis not caused by gonorrhea. Approximately 15 to 40 percent of NGU cases are caused by chlamydia. Another 15 to 25 percent of cases are caused by mycoplasma. However, NGU can be caused by other sexually transmitted infections such as Trichomonas vaginalis. The herpes simplex virus can also cause NGU.

A male patient staring out of the window

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NGU is a diagnosis of exclusion. That is, it doesn't tell what you are infected with. Instead, it tells you what you aren't infected with. In most cases, if you are diagnosed with NGU, further testing will be performed to try and identify the cause of the infection. However, with the exception of chlamydia, the bacteria that cause NGU can be hard to identify. Therefore, your healthcare provider may just decide to treat you with broad spectrum antibiotics.

It's particularly important to know that there is no widely available test for mycoplasma. Since it is one of the most common causes of NGU, that makes it hard for many people to get a diagnosis. Therefore, they may be treated according to mycoplasma treatment guidelines. That's particularly true if previous treatment for NGU has failed.

Who Gets NGU

NGU is diagnosed exclusively in people with penises. Although people with vaginas can have infections of the urethra, those infections are not generally caused by STDs. At least, urethra infections (urethritis) are not the primary reason STDs in women are diagnosed. Instead, the equivalent diagnosis in women is likely to be either cervicitis or bacterial vaginosis. Both of these can involve infections with the same types of bacteria that are sometimes responsible for NGU.


Thorough diagnosis for NGU may be based on urine tests or swabs. Usually, the initial diagnosis is based on visible symptoms of urethritis. (See attached NGU picture.) Then the healthcare provider has to rule out gonorrhea and chlamydia. If neither of those infections is the cause of the urethritis, it is often designated as NGU. However, some healthcare providers will engage in further testing to attempt to identify the pathogen responsible. Further testing is often indicated if the initial course of treatment does not get rid of the NGU.

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  • Centers for Disease Control and Prevention. Sexually Transmitted Diseases Treatment Guidelines, 2010. MMWR 2010;59(No. RR-12).

  • Centers for Disease Control and Prevention. Sexually Transmitted Diseases Treatment Guidelines, 2015.