Sexually transmitted diseases (STD's) are among the most common communicable diseases in the world. STD control mainly depends on tracing and treating all of the patient's sexual contacts. Educating the public and counseling patients about responsible sexual behavior are inevitable to prevent spreading. Commercial sex workers and persons with frequently changing sexual partners are at increased risk. Many infected people are carriers of a pathogen without subjective symptoms and are unknowingly transmitting the disease. Control of treatment to ensure that patients have been fully cured is often difficult to maintain, especially with commercial sex workers. Additionally, re-emergence of rare diseases, or the occurrence of drug-resistant strains, can be a result of an import of pathogens from other countries, e. g. the rapid spread of HIV infections in Europe and North America.

STD's include Neisseria gonorrhoeae (gonorrhea), Treponema pallidum (syphilis), Chlamydia trachomatis, unspecific urethritis, HIV infection, hepatitis, and others.

Gonorrhea, for instance, is an acute infection of the urogenital mucosa (and sometimes of the throat) which affects both men and women. The causing pathogen is called Neisseria gonorrheae (gonococci) and is transmitted by sexual practice. Women and homosexual men can be carriers without showing symptoms. Symptoms usually include discomfort and purulent discharge from urethrea, vagina or rectum, depending on the site of infection. Gonorrhoea can result in sterility.