Sexually transmitted (venereal) diseases are infections that are typically, but not exclusively, passed from person to person through sexual contact.
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.
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.
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
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, 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:
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).
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.
The following can help prevent STDs:
The only vaccines available are those for HPV infection and hepatitis A and B.
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.
Last full review/revision October 2008 by J. Allen McCutchan, MD, MSc