We all know the risks of unprotected sex, thanks to public education campaigns. And there have also been efforts to encourage people to seek an STD test, notably for chlamydia, which can cause infertility: another 200,000 people were diagnosed with it in the UK in 2008. Yet important elements in our society seem to encourage people not to find out whether they have an STD. Their sexual partners, meanwhile, would prefer not to contemplate it. So STDs are transmitted to people who have not had the opportunity to consent to that risk of infection.