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Overview of Sexually Transmitted Diseases

By J. Allen McCutchan, MD, MSc, University of California at San Diego

Sexually transmitted (venereal) diseases are infections that are typically, but not exclusively, passed from person to person through sexual contact.

  • Sexually transmitted diseases may be caused by bacteria, viruses, or protozoa.

  • Some infections can be spread through kissing or close body contact.

  • Some infections may spread to other parts of the body, sometimes with serious consequences.

  • Using condoms can help prevent these infections.

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) are relatively common. For example, in the United States, over 334,000 new cases of gonorrhea and over 1.4 million chlamydial infections were reported in 2012, and even more probably occur—making gonorrhea and chlamydial infections the two most common STDs.


Types of Sexually Transmitted Diseases




Chancroid (see Chancroid)

Chlamydial urethritis and cervicitis (see Chlamydial and Other Infections)

Gonorrhea (see Gonorrhea)

Granuloma inguinale (see Granuloma Inguinale)

Lymphogranuloma venereum (see Lymphogranuloma Venereum)

Syphilis (see Syphilis)


Genital herpes simplex (see Herpes Simplex Virus Infections)

Genital warts (caused by the human papillomavirus—see Genital Warts (Human Papillomavirus Infection, or HPV Infection))

Human immunodeficiency virus (HIV) infection or AIDS (see Human Immunodeficiency Virus (HIV) Infection)

Molluscum contagiosum (see Molluscum Contagiosum)

Parasitic (protozoan)

Trichomoniasis (see Trichomoniasis)


Pubic lice infestation (see Pubic lice)

Scabies (due to burrowing mites—see Scabies)

Many infectious organisms—from tiny viruses, bacteria, and parasites to visible insects (such as lice)—can be spread through sexual contact. Some infections, such as hepatitis A, B, and C and Salmonella infections (which cause diarrhea), can be transmitted during sexual activity, but they are often spread in other ways (see Other Sexually Transmitted Diseases). Thus, they are not typically considered STDs.


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

  • Kissing or close body contact—for pubic lice infestation, scabies, and molluscum contagiosum

  • From mother to child before or during birth—for syphilis, herpes, chlamydial infection, gonorrhea, human immunodeficiency virus (HIV) infection, and human papillomavirus (HPV) infection

  • Breastfeeding—for HIV infection

  • Contaminated medical instruments—for HIV infection


Symptoms 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.


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

  • Heart and brain infections due to syphilis

  • AIDS due to HIV

  • 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 (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 (see Pelvic Inflammatory Disease (PID)).

Pathway From the Vagina to the Ovaries

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.

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

  • Tightening of the foreskin, so that it cannot be pulled over the head of the penis

  • Narrowing of the urethra, blocking the flow of urine

  • 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: Male Reproductive Organs).

Pathway From the Penis to the Epididymis

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.

In both sexes, some STDs can cause persistent swelling of the genital tissues or infection of the rectum (proctitis).


  • Examination of a sample of blood, urine, or discharge

Doctors often suspect an STD based on symptoms. To identify the organism involved and thus confirm the diagnosis, doctors may take a sample of blood, urine, or discharge from the cervix 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). Other tests check for the presence of antibodies to the organism. 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.


The following can help prevent STDs:

  • Regular and correct use of condoms

  • 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

  • Circumcision (which can reduce the spread of HIV from women to men)

  • Prompt diagnosis and treatment of STDs (to prevent spread to other people)

  • Identification of the sexual contacts of infected people, followed by counseling or treatment of these contacts

The only vaccines available are those for HPV infection (see Human Papillomavirus Vaccine) and hepatitis A and B (see Hepatitis A Vaccine and Hepatitis B Vaccine).


  • Antibiotics or antiviral drugs depending on the STD

  • Simultaneous treatment of sex partners

Most STDs can be effectively treated with drugs. However, some new strains of bacteria and viruses, such as HIV, have become resistant to some drugs, making treatment more difficult. Resistance to drugs is likely to increase because drugs are sometimes misused (see Antibiotic resistance).

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, hepatitis B and C, and HIV infection, usually persist for life. Antiviral drugs can control but not yet cure all of these infections, except hepatitis C, which can be cured in some people after prolonged treatment.

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