Overview of Sexually Transmitted Infections
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
·
Syphilis
·
Lymphogranuloma
venereum
·
Granuloma
inguinale
·
Chlamydial,
mycoplasmal, and ureaplasmal infections
Viral
STIs include
·
Molluscum
contagiosum
Parasitic
infections that can be sexually transmitted include
·
Trichomoniasis
(caused by protozoa)
·
Scabies
(caused by mites)
·
Pediculosis
pubis (caused by lice)
Many
other infections not considered primarily to be STIs—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 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 B, and humanpapillomavirus infection.