The most crucial factors of STD risk are sexual behavior and activity, but female gender and specific social factors are important, as well (table 3).

Sexual Behavior
Over the past 30 years, the mean age of first sexual intercourse (

table 4) has decreased. Although in 1970 fewer than 5% of 15-year-olds had experienced sexual intercourse, in 1988 the average was already 26% and in 1995 37% of 15-year-olds were sexually active. This early sexual debut is associated with an increasing number of lifetime sexual partners (

table 5), which consequently also increases the risk of acquiring STDs. In the group of 15- to 18-year-olds the frequency of having more than 4 lifetime sexual partners increased from 18% in 1995 up to 44% in 2000.

Investigations of the risk of inconsistent use of contraceptives show that more than 50% of all adolescents do not use any contraception at their first sexual intercourse. Adolescents report the use of a condom (

table 5) during the most recent intercourse but this seems to be decreasing from the 54% reported in 1995. In any case, it should be noted that condoms do not deliver adequate protection from three of the most widespread STDs, namely HPV, HSV-2 and Chlamydia.

Adolescence is a period of intense sexual experimentation that includes both anal intercourse and homosexuality, which especially places these young people at high risk. In 1995 in Havana, 39% of 11- to 19-year-old girls and boys were found to have had experience in oral-genital sex and 21% in genital-anal sex. More striking, in 2000 in the USA, 74% of 14- to 17-year-olds were reported to have had oral-genital and 19% anal sex (

table 5). Epidemiologic studies have revealed significantly higher rates of syphilis, gonorrhea and venereal warts in particular in homosexual males than in heterosexuals. However, the incidence of both gonorrhea and syphilis among homosexuals has decreased since 1980 by up to 80% because of a re-evaluation of sexual practices as a response to the fear of AIDS.

Risk of Gender in Adolescence
Adolescent girls are reported to have the highest rates of STDs and the highest frequency of serious sequelae. On the one hand, this gender risk in adolescence is specifically caused by the characteristic instability of the hypothalamus- hypophysis-ovary axis, which results in a deficiency in progesterone that is in turn linked to an increased vulnerability of the female genital tract to infection. Thus, in adolescents still lacking efficient mucus and the typical absorbent activity of the cervix-ectropium, STD pathogens may settle, develop and ascend more readily into the upper tracts, thereby placing girls at a higher risk for pelvic inflammatory disease (PID).

On the other hand, other factors that contribute to more frequent STDs among females is their earlier start of sexual activity than boys’ and their tendency to have sex with older and more experienced partners, who are more likely to carry infections.

Social Reasons
Poor social circumstances and the resulting low quality of life essentially caused by the existing social structure are the most fundamental STD risk factors.

Adolescents in socially discriminated against ethnic and minority groups, as well as poor and unemployed adolescents, are reported to have earlier first sexual intercourse, more lifetime partners, and more intercourse without protection. These adolescents frequently use more alcohol and drugs like marijuana, crack or freebase cocaine prior to or during sex and, because of this, they may escalate into high-risk sexual behavior without, unfortunately, using any appropriate protection.

It is obvious, too, that these young people have little knowledge of STDs and their sequelae and little contact with the health care system.