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Overview of Sexually Transmitted Diseases

by J. Allen McCutchan, MD, MSc

Sexually transmitted diseases (STDs), also termed sexually transmitted infections (STIs), can be caused by a number of microorganisms that vary widely in size, life cycle, symptoms, and susceptibility to available treatments.

Bacterial STDs include syphilis, gonorrhea, chancroid, lymphogranuloma venereum, granuloma inguinale, and chlamydial, mycoplasmal, and Ureaplasma infections.

Viral STDs include genital and anorectal warts, genital herpes (see Herpesviruses:Mucocutaneous infection), molluscum contagiosum (see Molluscum Contagiosum), and HIV infection (see Human Immunodeficiency Virus (HIV)).

Parasitic infections that can be sexually transmitted include trichomoniasis (caused by protozoa—see Trichomoniasis), scabies (caused by mites—see Scabies), and pediculosis pubis (caused by lice—see Pubic lice).

Many other infections not considered primarily to be STDs—including salmonellosis, shigellosis, campylobacteriosis, amebiasis, giardiasis, hepatitis (A, B, and C), and cytomegalovirus infection—can be transmitted sexually.

Because sexual activity includes close contact with skin and mucous membranes of the genitals, mouth, and rectum, many organisms are efficiently spread between people. Some STDs cause inflammation (eg, in gonorrhea or chlamydial infection) or ulceration (eg, in herpes simplex, syphilis, or chancroid), which predispose to transmission of other infections (eg, HIV). STD prevalence rates remain high in most of the world, despite diagnostic and therapeutic advances that can rapidly render patients with many STDs noninfectious.

Factors impeding control of STDs include

  • Unprotected sexual activity with multiple partners

  • Difficulty talking about sexual issues for both physicians and patients

  • Inadequate funding for implementing existing diagnostic tests and treatments and for developing new tests and treatments

  • Susceptibility to reinfection if both partners are not treated simultaneously

  • Incomplete treatment, which can lead to development of drug-resistant organisms

  • International travel, which facilitates rapid global dissemination of STDs

Symptoms and signs vary depending on the infection. Many STDs cause genital lesions (see Differentiating Common Sexually Transmitted Genital Lesions).

Differentiating Common Sexually Transmitted Genital Lesions


Other Features


Solitary painless ulcer

Indurated, nontender or only slightly tender

Relatively nontender adenopathy

Syphilitic chancre

Clusters of small, painful superficial ulcers on an erythematous base

Sometimes with vesicles

Inguinal adenopathy

Herpes simplex virus infection

Shallow painful ulcer

Nonindurated, tender ulcers with ragged, undermined edges and a red border, varying in size and often coalescing

Regional adenopathy


Small papule or ulcer, often asymptomatic or unnoticed

Severely tender and painful adenopathy, sometimes with distal lymphedema or drainage to the skin

Sometimes fever

Lymphogranuloma venereum

Multiple, shallow ulcers

Characteristic extragenital lesions and burrows

Excoriated scabies

Multiple, shallow lesions

Visible lice, or egg sacs (nits) attached to hair shafts

Pediculosis pubis with excoriation

Elevated lesion

Velvety, malodorous, granulating lesions

No inguinal adenopathy

Granuloma inguinale

*Other causes of ulcers include mucous patches of secondary syphilis, erosive balanitis, gummatous ulceration of tertiary syphilis, Behçet syndrome, epithelioma, and trauma.

STDs are diagnosed and treated in a variety of settings; for many, diagnostic tests are limited or unavailable or patient follow-up is uncertain. Thus, identification of the causative organism is often not pursued, and initial treatment is often syndromic—ie, directed at the organisms most likely to cause the presenting syndrome (eg, urethritis, cervicitis, genital ulcers, pelvic inflammatory disease). Diagnostic testing is done more often when the diagnosis is unclear, when the infection is severe, when initial treatment is ineffective, or when other reasons (eg, public health surveillance, psychosocial reasons, including extreme mental distress and depression) are compelling.

STD control depends on

  • Adequate facilities and trained personnel for diagnosis and treatment

  • Public health programs for locating and treating recent sex partners of patients

  • Follow-up for treated patients to ensure that they have been cured

  • Education of health care practitioners and the public

  • Avoidance of high-risk behaviors by patients

Condoms and vaginal dams, if used correctly, greatly decrease risk of some STDs. Vaccines are unavailable for most STDs, except for hepatitis A and B and human papillomavirus infection.

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