sexually transmitted disease (STD) or venereal disease, term for infections acquired mainly through sexual contact. Five diseases were traditionally known as venereal diseases: gonorrhea, syphilis, and the less common granuloma inguinale, lymphogranuloma venereum, and chancroid. In the 1960s up to 20 other diseases were recognized as being transmitted by sexual contact, and the term "sexually transmitted disease" came into use. Some of the more common of these are AIDS, genital herpes (see herpes simplex), chlamydia, and human papillomavirus. Other diseases or infestations that can be transmitted sexually include giardiasis, amebiasis, scabies, pubic "crab" lice (see louse), hepatitis (A, B, and C), group B streptococcal infections (see streptococcus), cytomegalovirus infection, and the protozoan infection trichomoniasis.

STDs are generally graver in women, in whom diagnosis is often more difficult and treatment less available than for men; untreated they can lead to infertility or cause miscarriage, premature birth, or infection of the newborn. In some instances two or more infections may be present concurrently. The spread of sexually transmitted AIDS increased dramatically during the 1980s and continued through the 1990s. Other STDs are often seen in tandem with AIDS, partly because open sores that they produce can provide an easy route for the AIDS virus to enter the body. In the 2007 it was estimated that 19 million new cases of STDs were contracted in the United States each year.

Granuloma inguinale is caused by Calymmatobacterium granulomatis and is common in tropical and subtropical regions. Early lesions appear as painless, red, open sores on the skin of the genital and pelvic regions, succeeded by a spreading ulceration of the tissues. If not treated, the condition becomes chronic and may lead to death through anemia and general debility. Antibiotics such as tetracycline can eliminate the infection.

Lymphogranuloma venereum, also common in tropical and subtropical regions, is caused by a strain of Chlamydia trachomatis, an organism classified as a bacterium but having some viral characteristics. The primary genital lesion is often overlooked. The lymphatic structures about the pelvic and rectal region then become involved; blockage of such structures may cause disfigurement and scarring of external genitals. Fever and headache are other constitutional symptoms. Severe involvement of the rectal mucosa may cause intestinal obstruction or stricture. Tetracycline is the drug of choice, although other antibiotics are effective.

Chancroid is an acute localized infection caused by a bacterium called Hemophilus ducreyi. It can result in painful ulcerations of the skin, usually in the groin. In women symptoms may be absent or limited to painful urination, defecation, or intercourse. Involvement of the lymph nodes occurs in more than half the cases. Usually the disease is self-limited, but it may cause severe destruction of tissue. Antibiotics have been effective in treatment, but resistant strains are an increasing problem.

In order to reduce ignorance and thereby decrease the risk of venereal infection, the U.S. government just before and after World War II encouraged publicity on the matter, for the taboo long associated with public discussion of these contagious diseases had given rise to serious public-health problems. A nationwide campaign was initiated in 1937 by Thomas Parran, then serving as U.S. surgeon general, to educate the public about the incidence, cause, and cure of venereal diseases. As a result, the number of new cases in the United States steadily declined each year until the 1950s, when a rise was noted, especially among teenagers and young adults. In 1998, concerned by high U.S. rates of such common STDs as human papillomavirus, genital herpes, and chlamydia, as well as local outbreaks of syphilis and gonorrhea, the Centers for Disease Control and Prevention began a new far-reaching campaign to combat STDs.

Public authorities and private agencies coordinate their efforts to identify and isolate promptly all sources of infection. Worldwide, despite advances in diagnosis and treatment, the incidence of STDs has continued to rise and has reached epidemic proportions in many countries. Among the factors believed responsible for increases are changes in sexual behavior (e.g., the use of oral contraceptives), the emergence of drug-resistant strains, symptomless carriers, a highly mobile population, lack of public education, and the reluctance of patients to seek treatment.

See T. Rosebury, Microbes and Morals (1971); K. L. Jones et al., VD (1974); J. Jacobson, Women's Reproductive Health (1991).