Statistically abstinence does not completely prevent sexually transmitted diseases, why?

Other contact or lie: Well, some people say they are abstinent and arent. I have teens who are pregnany ever month who swear they are having sex. Ooops! also, some people say they are not sexually active because they only have oral (or anal or other) sex, which is still a risk for spread of stds. For instance, 75% of sexually active teen girls with hpv genital lesions have hpv in their mouth! oral sex spreads hpv.

Definition of Sex: When people are asked what abstinence means, their answers range from no penetration or oral sex up to "anal is ok, just not vaginal sex". Given that the definition is in doubt, it's not unexpected that stds can still occur in abstaining people via oral sex, mutual masturbation or even anal penetration.