Sexually transmitted infections (STI) are a major global cause of acute illness, infertility, long-term disability and death, with severe medical and psychological consequences for millions of men, women and infants.

STIs may produce no symptoms at all or produce symptoms that are mild and transient.  However, many STIs can have severe long-term consequences. Some (gonorrhea, chancroid, herpes simplex virus) produce acute symptoms. In adults, chlamydia and gonorrhea may lead to complications such as infertility and potentially fatal ectopic pregnancy or chronic illness. In unborn and newborn children, chlamydia, gonorrhea and syphilis can produce serious and often life-threatening conditions, such as congenital syphilis, pneumonia and low birth weight. Infection with the human papillomavirus (HPV) is a proven precondition for the development of carcinoma of the cervix, which is the second leading cause of female cancer mortality worldwide.

Cases of syphilis and gonorrhea have now reached epidemic levels in eastern Europe and central Asia. This presents a major public health problem, as well as a potentially important co-factor of sexual transmission of HIV. In western Europe, the incidence of reported syphilis is below 2 per 100 000 and gonorrhoea is below 20 per 100 000.