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, the diseases and symptoms caused, and susceptibility to available treatments.
Bacterial STDs include
Viral STDs include
Parasitic infections that can be sexually transmitted include
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Trichomoniasis (caused by protozoa)
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Scabies (caused by mites)
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Pediculosis pubis (caused by lice)
Many other infections not considered primarily to be STDs—including salmonellosis, shigellosis, campylobacteriosis, amebiasis, giardiasis, hepatitis (A, B, and C), Zika virus infection, 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. In the US, an estimated 20 million new cases of STDs occur each year; about half occur in people aged 15 to 24 years (see also Centers for Disease Control and Prevention [CDC]: Sexually Transmitted Disease Surveillance 2018).
Factors impeding control of STDs include
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Unprotected sexual activity with multiple partners
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Difficulty talking about sexual issues for both physicians and patients
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Inadequate funding for implementing existing diagnostic tests and treatments and for developing new tests and treatments
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Susceptibility to reinfection if both partners are not treated simultaneously
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Incomplete treatment, which can lead to development of drug-resistant organisms
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International travel, which facilitates rapid global dissemination of STDs
Symptoms and Signs of STDs
Symptoms and signs of STDs vary depending on the infection. Many STDs cause genital lesions (see table Differentiating Common Sexually Transmitted Genital Lesions).
Differentiating Common Sexually Transmitted Genital Lesions
Finding |
Other Features |
Cause* |
|
Solitary painless ulcer |
Indurated, nontender or only slightly tender Relatively nontender adenopathy |
|
|
Clusters of small, painful superficial ulcers on an erythematous base |
Sometimes with vesicles Inguinal adenopathy |
|
|
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 |
|
|
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 nodule that ulcerates and progressively expands |
Velvety, malodorous, granulating lesions No inguinal adenopathy |
|
|
* Other causes of ulcers include mucous patches of secondary syphilis, erosive balanitis, gummatous ulceration of tertiary syphilis, Behçet syndrome, epithelioma, and trauma. |
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Diagnosis of STDs
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. Often, diagnosis is based only on clinical findings.
Diagnostic testing may include Gram staining and culture or laboratory tests such as nucleic acid amplification tests (NAATs). Diagnostic testing is done more often in the following situations:
Treatment of STDs
Because diagnostic tests are often limited or unavailable and/or patient follow-up is uncertain, 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).
Most STDs can be effectively treated with drugs. However, drug resistance is an increasing problem.
Patients who are being treated for a bacterial STD should abstain from sexual intercourse until the infection has been eliminated from them and their sex partners. Sex partners should be evaluated and treated simultaneously.
Viral STDs, especially herpes and HIV infection, usually persist for life. Antiviral drugs can control but not yet cure all of these infections.
Prevention of STDs
STD control depends on
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Adequate facilities and trained personnel for diagnosis and treatment
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Public health programs for locating and treating recent sex partners of patients
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Follow-up for treated patients to ensure that they have been cured
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Education of health care practitioners and the public
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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, hepatitis B, and human papillomavirus infection.
More Information about STDs
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
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CDC: Sexually Transmitted Disease Surveillance 2018: Reference document with statistics and trends for STDs in the US through 2018 for policy makers, researchers, and others who are concerned with the public health implications of these diseases
