Sexually transmitted infections (STIs), also termed sexually transmitted diseases or STDs, 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 STIs include
Chlamydial, mycoplasmal, and ureaplasmal infections Chlamydial, Mycoplasmal, and Ureaplasmal Mucosal Infections Sexually transmitted urethritis, cervicitis, proctitis, and pharyngitis not due to gonorrhea are caused predominantly by chlamydiae and infrequently by mycoplasmas or Ureaplasma sp. Chlamydiae... read more
Viral STIs include
Parasitic infections that can be sexually transmitted include
Many other infections not considered primarily to be STIs—including salmonellosis Overview of Salmonella Infections The genus Salmonella is divided into 2 species, S. enterica and S. bongori, which include > 2500 known serotypes. Some of these serotypes are named. In such cases, common... read more , shigellosis Shigellosis Shigellosis is an acute infection of the intestine caused by the gram-negative Shigella species. Symptoms include fever, nausea, vomiting, tenesmus, and diarrhea that is usually bloody... read more , campylobacteriosis Campylobacter and Related Infections Campylobacter infections typically cause self-limited diarrhea but occasionally cause bacteremia, with consequent endocarditis, osteomyelitis, or septic arthritis. Diagnosis is by culture... read more , amebiasis Amebiasis Amebiasis is infection with Entamoeba histolytica. It is acquired by fecal-oral transmission. Infection is commonly asymptomatic, but symptoms ranging from mild diarrhea to severe dysentery... read more , giardiasis Giardiasis Giardiasis is infection with the flagellated protozoan Giardia duodenalis (G. lamblia, G. intestinalis). Infection can be asymptomatic or cause symptoms ranging from intermittent... read more , hepatitis Overview of Acute Viral Hepatitis Acute viral hepatitis is diffuse liver inflammation caused by specific hepatotropic viruses that have diverse modes of transmission and epidemiologies. A nonspecific viral prodrome is followed... read more (A, B, and C), Zika virus infection Zika Virus (ZV) Infections The Zika virus is a mosquito-borne flavivirus that is antigenically and structurally similar to the viruses that cause dengue, yellow fever, and West Nile virus. Zika virus infection is typically... read more , and cytomegalovirus infection Cytomegalovirus (CMV) Infection Cytomegalovirus (CMV, human herpesvirus type 5) can cause infections that have a wide range of severity. A syndrome of infectious mononucleosis that lacks severe pharyngitis is common. Severe... read more —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 STIs 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).
STI prevalence rates remain high in most of the world, despite diagnostic and therapeutic advances that can rapidly render patients with many STIs noninfectious. In the US, an estimated 20 million new cases of STIs 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 STIs 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 STIs
Symptoms and Signs of STIs
Symptoms and signs of STIs vary depending on the infection. Many STIs cause genital lesions (see table Differentiating Common Sexually Transmitted Genital Lesions Differentiating Common Sexually Transmitted Genital Lesions 
).
Diagnosis of STIs
Often clinical evaluation
Gram staining and culture
Laboratory tests
STIs 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:
The diagnosis is unclear.
The infection is severe.
Initial treatment is ineffective.
Other reasons (eg, public health surveillance, psychosocial reasons, including extreme mental distress and depression) are compelling.
Treatment of STIs
Syndromic treatment
Sometimes antimicrobials
Simultaneous treatment of sex partners
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 STIs can be effectively treated with drugs. However, drug resistance is an increasing problem.
Patients who are being treated for a bacterial STI 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 STIs, especially herpes and HIV infection, usually persist for life. Antiviral drugs can control but not yet cure all of these infections.
Prevention of STIs
STI 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 STIs.
Vaccines are unavailable for most STIs, except for hepatitis A Hepatitis A (HepA) Vaccine Both hepatitis A vaccines provide long-term protection against hepatitis A. For more information, see Hepatitis A Advisory Committee on Immunization Practices Vaccine Recommendations and Centers... read more , hepatitis B Hepatitis B (HepB) Vaccine The hepatitis B vaccine is 80 to 100% effective in preventing infection or clinical hepatitis B in people who complete the vaccine series. For more information, see Hepatitis B Advisory Committee... read more , and human papillomavirus infection Human Papillomavirus (HPV) Vaccine Human papillomavirus (HPV) infection is the most common sexually transmitted disease. HPV can cause skin warts, genital warts, or certain cancers, depending on the type of HPV. Vaccines are... read more .
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
CDC: Sexually Transmitted Disease Surveillance 2018: Reference document with statistics and trends for STIs in the US through 2018 for policy makers, researchers, and others who are concerned with the public health implications of these diseases
