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, 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.
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
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
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 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)).
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
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—Fig. 1: Male Reproductive Organs).
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. 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:
The only vaccines available are those for HPV infection (see Human Papillomavirus) and hepatitis A and B (see Hepatitis A and xref.discussed-in Hepatitis 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. 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.
Last full review/revision December 2014 by J. Allen McCutchan, MD, MSc