Sexually transmitted infections (STIs) are among the most common communicable conditions and affect the health and lives of people worldwide. More than 30 pathogens can be transmitted sexually, and individuals may have multiple infections at the same time.

Individuals who are infected with an STI may not be aware of their infection but can transmit the infection to others and may go on to develop long term and potentially fatal outcomes including cancer, chronic pelvic pain, ectopic pregnancies, and infertility.  STIs can also be transmitted vertically from mother to infant during pregnancy or at delivery with potential adverse consequences for the infant.  Infection with one STI may also facilitate the transmission of other STIs, including HIV.

The World Health Organization produces global and regional estimates of the prevalence and incidence of four of the most common curable STIs in adults 15 to 49 years of age: chlamydia (etiological agent: Chlamydia trachomatis), gonorrhoea (Neisseria gonorrhoeae) and trichomoniasis (Trichomonas vaginalis) every 4 to 5 years, and estimates of syphilis (Treponema pallidum) every 2 to 3 years.