Almost always sex. Non-gonococcal urethritis or ngu, sometimes known as nsuis almost caused through sexual contact. The most common cause is bacterial duie to chlamydia, and less commonly ureaplasma, hemophylus or mycoplasma. Trichcomonas, a parasitic infection and rarely herpes (a virus) can be causative. Ureaplasma ngu can be transmitted without sex. Non infectious causes are catheterization or spermicidal cream.