In the United Kingdom, NGU is more often called non-specific urethritis; "non-specific" is a medical term meaning "specific cause has not been identified", and in this case refers to the detection of urethritis, and the testing for but found negative of gonorrhea. In this sense, the most likely cause of NSU is a chlamydia infection.
However, the term NSU is sometimes distinguished and used to mean that both gonorrhea and chlamydia have been ruled out. Thus, depending on the sense, chlamydia can either be the most likely cause or have been ruled out, and frequently detected organisms are ureaplasma urealyticum and mycoplasma hominis.
Read more about this topic: Non-gonococcal Urethritis