Oral sex as a risk factor for Chlamydia-negative ureaplasma-negative nongonococcal urethritis.

We present a case-control study that evaluated the association of Chlamydia-negative, Ureaplasma-negative nongonococcal urethritis with oral and/or anal sex. The study population was composed of 120 patients diagnosed as having nongonococcal urethritis in the Diagnostic Center for sexually transmitted diseases (STD) of the Medical School of Seville. Cases were 56 men suffering from nonogonococcal urethritis from whom neither Chlamydia trachomatis nor Ureaplasma urealyticum was isolated; the remaining 64 males with cultures positive for these agents were considered as controls. Insertive genital-oral intercourse significantly increased the risk of Chlamydia-negative, Ureaplasma-negative nongonococcal urethritis (odds ratio, 11.400; 95% confidence interval, 2.357-75.057). This association was still very strong (odds ratio, 8.882) after adjustment for homosexuality. Insertive anal intercourse appears not to increase the risk of Chlamydia-negative, Ureaplasma-negative nongonococcal urethritis. We conclude that insertive oral sex can be an important risk factor in the development of nongonnococcal urethritis in which the microbial agent is still unknown.