STD incidence rates remain high in most of the world, despite diagnostic and therapeutic advances that can rapidly render patients with many STDs noninfectious and cure most. In many cultures, changing sexual morals and oral contraceptive use have eliminated traditional sexual restraints, especially for women, and both physicians and patients have difficulty dealing openly and candidly with sexual issues. Additionally, development and spread of drug-resistant bacteria (e.g., penicillin-resistant gonococci) makes some STDs harder to cure. The effect of travel is most dramatically illustrated by the rapid spread of the AIDS virus (HIV-1) from Africa to Europe and the Americas in the late 1970s.
In 1996, the World Health Organization estimated that more than 1 million people were being infected daily. About 60% of these infections occur in young people <25 years of age, and of these 30% are <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. An estimated 340 million new cases of syphilis, gonorrhea, chlamydia and trichomoniasis occurred throughout the world in 1999.
Commonly reported prevalences of STIs among sexually active adolescent girls both with and without lower genital tract symptoms include chlamydia (10–25%), gonorrhea (3–18%), syphilis (0–3%), Trichomonas vaginalis (8–16%), and herpes simplex virus (2–12%). Among adolescent boys with no symptoms of urethritis, isolation rates include chlamydia (9–11%) and gonorrhea (2–3%).
At least one in four U.S. teenage girls has a sexually transmitted disease, a CDC study found. Among girls who admitted ever having sex, the rate was 40%.AIDS is the single largest cause of mortality in present-day Sub-Saharan Africa. The majority of HIV infections are acquired through unprotected sexual relations between partners, one of whom has HIV. Approximately 1.1 million persons are living with HIV/AIDS in the United States, and AIDS remains the leading cause of death among African American women between ages 25 and 34. Hepatitis B is also classed as a sexually transmitted disease because it can be passed on sexually. The disease is found globally, with the highest rates in Asia and Africa and lower rates in the Americas and Europe. Worldwide, an estimated two billion people have been infected with the hepatitis B virus.