Diseases that are transmitted by sexual behavior are caused by infection with bacteria, viruses, parasites, fungi and protozoa that are transmitted from infected genitalia. The most dangerous sexually transmitted diseases (STDs), the HIV and 50% of hepatitis B are well known to be transmitted invasively only by secretions or blood containing the virus. This means that such transmissions do not depend exclusively on sexual contact, although in all likelihood microlesions can be caused by sexual behavior. Though there is a lack of worldwide, evidence-based epidemiologic data, published trends show that STDs are a significant health problem both in developed and developing countries. As early as 1996, WHO estimated that more than 1 million people were being infected daily (table 1). About 60% of these infections occur in young people <25 years of age, and 30% of this age group is <20 years. Between the ages of 14 and 19, STDs occur more frequently in girls than boys by a ratio of nearly 2:1; this equalizes by age 20.

Pediatric and Adolescent Gynecology  1. Gynecologic Clinical Examination of the Child and Adolescent  2. Imaging in Pediatric and Adolescent Gynecology  3. The Prepubertal Girl     L Ambiguous Genitalia in the Newborn: Diagnosis, Etiology and Sex Assignment     L Vulvo-Vaginal Disorders     L Precocious Puberty (Complete, Partial)     L Ovarian Cysts in Prepubertal Girls     L Sexual Abuse in Prepubertal Children and Adolescents  4. The Adolescent Girl     L Delayed Puberty     L Menstrual Irregularities     L Adolescent Dysmenorrhea     L Hyperandrogenism in Adolescent Girls     L Ovarian Masses in Adolescent Girls     L Breast Diseases in Adolescents     L Chronic Pelvic Pain and Recurrent Abdominal Pain     L Contraception for Adolescents     L Teenage Pregnancy

The yearly rate of new cases of viral hepatitis B is estimated at 20 million, and it is presumed that 350 million people are chronically infected, particularly in Africa and Asia, meaning 3 - 5% of the world's population. In 2000, 53 million people were registered as being infected with HIV, with 95% of them in developing countries. Besides HIV and hepatitis B, more than 20 other types of STDs are known, the most common of which are infections of Chlamydia, Neisseria gonorrhoeae, human papilloma virus (HPV), herpes simplex virus (HSV-1, HSV-2) and syphilis (table 2). It should not be necessary to emphasize that infection by one STD tends to increase the risk of infection by other STDs.

Epidemiologic trends for STDs obviously differ throughout the world and mostly depend on escalating contradictions in social developments. A good example is the huge social changes in socialist countries as they open and adapt to the market economy: The 3-fold increase in gonorrhea and 20-fold increase in syphilis from 1989 to 1998 in the People's Republic of China is similar to findings in Mongolia. The changed situation in Lithuania of the former Soviet Union is also symptomatic, where a 10-fold increase in gonorrhea and a 50-fold increase in syphilis were registered from 1990 to 1996. The increase in syphilis in 18- to 19-year-old women, however, is reported to have grown 200-fold.

The very different frequencies of STDs that have been reported are mostly caused by different diagnostic methods with more or less sensitivity and selectivity (see table 11). Another significant problem is the often too small size of the samples selected for the spot checks. Specific determinants of STD epidemiology include sexual education, sexual behavior, and demographic and sociological factors, as well as such crucial, quality of health care factors as accessible pharmaceutics, available diagnostic and screening methods and treatment. The synergy of these factors ultimately determines the incidence of sexually transmitted infections and their complications.

Adolescents, and particularly those who are already sexually active, are at higher risk of acquiring STDs because of a lack of knowledge and sexual education.