According to the World Health Organization, as of November 2013, there are over 30 distinct bacteria, parasites and viruses that are mainly transmitted by means of anal, oral and vaginal sex. Over 1 million new cases of sexually transmitted infections (STIs) occur each day.
According to the WHO, around 500 million people acquire chlamydia, gonorrhoea, syphilis and trichomoniasis infections every year. Around 530 million people are infected with HSV2, the virus that leads to genital herpes. Another common STI is the human papillomavirus (HPV), present in more than 290 million women worldwide. Some STIs, such as gonorrhoea, are becoming more resistant to treatment. STIs are not exclusively transmitted sexually. They can also be transmitted through blood transfusions, tissue transfer and during childbirth and pregnancy.