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, an estimated 360,000 cases of gonorrhea and over 1 million chlamydial infections are reported, and even more probably occur every year in the United States—making them the two most common STDs.

Causes

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

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Types of Sexually Transmitted Diseases Type Disease Bacterial Chancroid Chlamydial urethritis and cervicitis Gonorrhea Granuloma inguinale Lymphogranuloma venereum Syphilis Viral Genital herpes simplex (see Viral Infections: Herpes Simplex Virus Infections) Genital warts (caused by the human papillomavirus) Molluscum contagiosum (see Viral Skin Infections: Molluscum Contagiosum) Human immunodeficiency virus (HIV) infection or AIDS (see Human Immunodeficiency Virus HIV Infection: Human Immunodeficiency Virus Infection) Parasitic (protozoan) Trichomoniasis Insect Pubic lice infestation Scabies (due to burrowing mites)

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

• 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

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.

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 heart and brain infections due to syphilis, AIDS due to HIV, and cervical cancer due to HPV.

In women, some organisms that enter the vagina can move up the vagina to the cervix (the lower part of the uterus), enter the uterus, and reach the fallopian tubes and sometimes the ovaries (see Biology of the Female Reproductive System: Internal Female Genital Organs). 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. These infections are considered pelvic inflammatory disease (see Vaginal Infections and Pelvic Inflammatory Disease).

In men, organisms that enter through the penis may infect the tube that carries urine from the bladder through the penis (urethra). Complications that can result from chronic infection of the urethra include the following:

• 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 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 Biology of the Male Reproductive System:Structure of the Male Reproductive System).

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

Diagnosis

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 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. Sometimes genetic testing is required to identify the organism's unique genetic material. Other tests vary depending on the STD suspected.

Prevention

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 partners who have other sex partners or with prostitutes
• 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 followed by counseling or treatment of the sexual contacts of infected people

The only vaccines available are those for HPV infection and hepatitis A and B.

Treatment

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. As new drugs are developed and more people are treated, resistance to drugs is likely to increase (see Bacterial Infections: 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.

How to Use a Condom
Use a new condom for each act of sexual intercourse. Use the correct size condom. Carefully handle the condom to avoid damaging it with fingernails, teeth, or other sharp objects. Put the condom on after the penis is erect and before any genital contact with the partner. Place the rolled condom over the tip of the erect penis. Leave ½ inch at the tip of the condom to collect semen. With one hand, squeeze trapped air out of the tip of the condom. If uncircumcised, pull the foreskin back before unrolling the condom. With the other hand, roll the condom over the penis to its base and smooth out any air bubbles. Make sure that lubrication is adequate during intercourse. With latex condoms, use only water-based lubricants. Oil-based lubricants (such as petroleum jelly, shortening, mineral oil, massage oils, body lotions, and cooking oil) can weaken latex and cause the condom to break. Hold the condom firmly against the base of the penis during withdrawal, and withdraw the penis while it is still erect to prevent slippage.

Last full review/revision October 2008 by J. Allen McCutchan, MD, MSc