Topic Resources
Sexually transmitted
(venereal) diseases are infections that are typically, but not
exclusively, passed from person to person through sexual contact.
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Sexually transmitted diseases may be caused by bacteria, viruses, or protozoa.
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Some infections can be spread through kissing or close body contact.
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Some infections may spread to other parts of the body, sometimes with serious consequences.
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Using condoms can help prevent these infections.
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Most sexually transmitted diseases can be effectively treated with drugs.
Sexual intercourse provides an easy opportunity for organisms to spread (be transmitted) from one person to another because it involves close contact and transfer of genital and other body fluids.
Sexually transmitted diseases (STDs), also called sexually
transmitted infections (STIs), are relatively common. For example, an
estimated 20 million new cases of STDs occur each year in the United
States. About half of the new cases occur in people aged 15 to 24 years.
Over 460,000 new cases of gonorrhea and almost 1.6 million chlamydial
infections were reported in 2016, and even more probably occur—making
gonorrhea and chlamydial infections the two most common STDs.
Several factors make prevention of STDs difficult. They include the following:
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Unprotected sexual activity with several partners (whose names may be unknown and who thus may be difficult to find)
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Reluctance to talk about sexual issues with a health care practitioner
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The need for more funding to identify and treat as many infected people as possible and to develop better diagnostic tests and treatments for STDs
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The need to treat both sex partners simultaneously if one of them is infected
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Incomplete treatment, which can lead to development of organisms that are resistant to drugs
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International travel, which enables STDs to be rapidly spread worldwide
Causes
Many infectious organisms—from tiny viruses, bacteria, and parasites to visible insects (such as lice)—can be spread through sexual contact. Some infections can be transmitted during sexual activity, but they are often spread in other ways. Thus, they are not typically considered STDs. These infections include hepatitis A, B, and C and infections of the digestive tract (which cause diarrhea), such as Salmonella infections, Campylobacter infections, shigellosis, giardiasis, and amebiasis.
Transmission
Although STDs usually result from having vaginal, oral, or anal sex with an infected partner, genital penetration is not necessary to spread an infection. Some STDs can be spread in other ways, including
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From mother to child before or during birth—for syphilis, herpes, chlamydial infection, gonorrhea, human immunodeficiency virus (HIV) infection, and human papillomavirus (HPV) infection
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Breastfeeding—for HIV infection
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Contaminated medical instruments—for HIV infection
Symptoms
Symptoms of STDs vary greatly, but the first symptoms usually
involve the area where the organisms entered the body. For example,
sores may form in the genital area or mouth. There may be a discharge
from the penis or the vagina, and urination may be painful.
Genital Sore
Image courtesy of Dr. Pirozzi via the Public Health Image Library of the Centers for Disease Control and Prevention.
Some of the symptoms increase the risk of getting other
infections (such as HIV infection). For example, having irritated skin
(inflammation, as occurs in gonorrhea or chlamydial infection) or sores
(as occurs in herpes, syphilis, or chancroid) makes it easier for other
infectious organisms to enter the body.
Complications
When STDs are not diagnosed and treated promptly, some organisms
can spread through the bloodstream and infect internal organs, sometimes
causing serious, even life-threatening problems. Such problems include
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Cardiovascular (heart and blood vessel) and brain infections due to syphilis
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AIDS due to HIV
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Cervical, rectal, anal, and throat cancer due to HPV
In women, some organisms that enter the vagina can infect
other reproductive organs. The organisms can infect the cervix (the
lower part of the uterus that forms the end of the vagina), enter the
uterus, and reach the fallopian tubes and sometimes the ovaries (see
Figure: Pathway From the Vagina to the Ovaries).
Damage to the uterus and fallopian tubes can result in infertility or a
mislocated (ectopic) pregnancy. The infection may spread to the
membrane that lines the abdominal cavity (peritoneum), causing
peritonitis. Infections of the uterus, fallopian tubes, ovaries, and/or
peritoneum are called pelvic inflammatory disease.
Pathway From the Vagina to the Ovaries
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In women, some organisms can enter the vagina and infect other
reproductive organs. From the vagina, these organisms can enter the
cervix and uterus and may reach the fallopian tubes and sometimes the
ovaries.
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In men, organisms that enter through the penis may infect
the tube that carries urine from the bladder through the penis
(urethra). Complications are uncommon if infections are treated quickly,
but chronic infection of the urethra can cause the following:
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Tightening of the foreskin, so that it cannot be pulled over the head of the penis
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Narrowing of the urethra, blocking the flow of urine
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Development of an abnormal channel (fistula) between the urethra and the skin of the penis
Occasionally in men, organisms spread up the urethra and travel
through the tube that carries sperm from the testis (ejaculatory duct
and vas deferens) to infect the epididymis (the coiled tube on top of
each testis—see Figure: Pathway From the Penis to the Epididymis).
Pathway From the Penis to the Epididymis
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Occasionally in men, organisms spread up the urethra and travel
through the tube that carries sperm from the testis (vas deferens) to
infect the epididymis at the top of a testis.
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In both sexes, some STDs can cause persistent swelling of the genital tissues or infection of the rectum (proctitis).
Diagnosis
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A doctor's evaluation
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Examination of a sample of blood, urine, or discharge
Doctors often suspect an STD based on symptoms.
For many STDs, tests to identify the cause are limited or
unavailable. Thus, doctors sometimes do not do tests to identify the
cause. Instead, they choose treatment based on which organisms are most
likely to cause the person's symptoms. Also, doctors may treat people at
their first visit, before test results become available (which usually
takes several days), in case they do not come back after test results
are available.
To identify the organism involved and thus confirm the diagnosis,
doctors may take a sample of blood, urine, or discharge from the vagina
or penis and examine it. The sample may be sent to a laboratory for the
organisms to be grown (cultured) to aid in identification.
Some tests for STDs are designed to identify the organism’s
unique genetic material (DNA or RNA). Sometimes techniques that increase
the amount of the bacteria's genetic material are used. These tests are
called nucleic acid amplification tests (NAATS). Because these
techniques make the organisms easier to detect, urine samples can be
used. Other tests check for the presence of antibodies that are produced
by the immune system in response to the specific organism that is
causing the infection. Doctors choose the type of test based on the STD
suspected.
If a person has one STD, such as gonorrhea, doctors also do tests
for other STDs, such as chlamydial infection, syphilis, and HIV
infection. Doctors do these other tests because people who have one STD
have a relatively high chance of having another one.
Prevention
The following can help prevent STDs:
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Regular and correct use of condoms
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Avoidance of unsafe sex practices, such as frequently changing sex partners or having sexual intercourse with prostitutes or with partners who have other sex partners
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Circumcision (which can reduce the spread of HIV from women to men)
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Prompt diagnosis and treatment of STDs (to prevent spread to other people)
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Identification of the sexual contacts of infected people, followed by counseling or treatment of these contacts
Not having sex (anal, vaginal, or oral) is the most reliable way to prevent STDs but is often unrealistic.
How to Put on a Condom
Treatment
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Antibiotics or antiviral drugs depending on the STD
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Simultaneous treatment of sex partners
Most STDs can be effectively treated with drugs (antibiotics for
bacterial infections and antiviral drugs for viral infections). However,
some new strains of bacteria and viruses have become resistant to some
drugs, making treatment more difficult. Resistance to drugs is likely to increase because drugs are sometimes misused.
People 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. Thus, sex partners should be tested and
treated simultaneously.
Viral STDs, especially herpes and HIV infection, usually persist
for life. Antiviral drugs can control but not yet cure these infections.
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