Because so few people practice oral-penile sex to the exclusion of other sexual practices, it is extremely tough to recruit and retain subjects for epidemiologic research of the HIV danger related to this practice. Only one examine was in a position to do that ; one other examined monogamous serodiscordant couples whose solely unprotected sexual exercise was oral sex. Despite the case stories, the epidemiologic evidence suggests that unprotected oral-penile intercourse is a low-threat exercise. Estimating precise per-act threat is difficult as a result of so few folks follow oral sex to the exclusion of different, higher-threat sexual activities. Most research of male-to-female and feminine-to-male transmission additionally failed to show any increased risk of HIV an infection related to oral-penile sex.