Sexually transmitted diseases (STDs) are caused by a group of infectious microorganisms that are transmitted mainly through sexual activity. These agents represent a costly, burdensome global public health problem. STDs can cause harmful, often irreversible, clinical complications, including reproductive health problems, fetal and perinatal health problems, and cancer, and they are also linked in a causal chain of events to the sexual transmission of human immunodeficiency virus (HIV) infection. Although STDs are largely preventable through behavior modification and sound primary health care, they are under-recognized and under-appreciated as a public health problem by most healthcare providers, the general public, and healthcare policy makers. In 1997, the Institute of Medicine characterized STDs as "hidden epidemics of tremendous health and economic consequence" in the United States and advocated urgent national preventive action.
An estimated 333 million curable STDs occur annually worldwide. In the United States, STDs are among the most frequently reported infectious diseases nationwide. Each year an estimated 15 million new cases of STDs occur in Americans, including nearly 4 million infections in U.S. teenagers. The annual direct and indirect costs of the principal STDs, including sexually transmitted HIV infection, and their complications are estimated at $17 billion.
More than twenty-five bacteria, viruses, protozoa, and yeasts are considered sexually transmissible. Bacterial STDs include those caused by Chlamydia trachomatis (chlamydia), Neisseria gonorrhoeae (gonorrhea), Treponema pallidum (syphilis), Haemophilus ducreyi (chancroid), and other common sexually transmitted organisms. Chlamydia and gonorrhea cause inflammatory reactions in the host. In women, these organisms can ascend into the upper reproductive tract where pelvic inflammatory disease (PID) can cause irreparable damage to the reproductive organs and result in infertility, ectopic pregnancy, and chronic pelvic pain. In its early stages, syphilis causes painless genital ulcers and other infectious lesions. Left untreated, syphilis moves through the body in stages, damaging many organs over time. Chancroid is associated with painful genital lesions. In pregnant women, acute bacterial STDs can cause potentially fatal congenital infections or perinatal complications, such as eye and lung infections in the newborn. Effective single-dose antimicrobials can cure chlamydia, gonorrhea, syphilis, and chancroid.
Viral STDs include the sexually transmitted viral infections caused by human immunodeficiency virus (HIV infection), herpes simplex virus type 2 (genital herpes), and human papillomavirus (HPV infection). Initial infections with these organisms may be asymptomatic or cause only mild symptoms. Treatable but not curable, viral STDs appear to be lifelong infections. HIV is the virus that causes acquired immunodeficiency syndrome (AIDS). Herpes causes periodic outbreaks of painful genital lesions. Some strains of HPV cause genital warts, and others are important risk factors for cervical dysplasia and invasive cervical cancer. Hepatitis B virus (HBV) is another acute viral illness that can be transmitted through sexual activity. Most persons who acquire HBV infection recover and have no complications, but it can sometimes become a chronic health problem.