A sexually transmitted disease (STD) is a disease caused by a pathogen (i.e., a disease-causing virus, bacterium, parasite, fungus) that is spread from person to person primarily through sexual contact. STDs can be painful, irritating, debilitating, and life threatening. More than twenty sexually transmitted diseases have been identified.

Incidence and Prevalence

STDs occur most commonly in sexually active teenagers and young adults, especially those with multiple sex partners. An estimated 200 to 400 million people worldwide are infected—representing men and women of all economic classes.

According to the U.S. Department of Health and human Services, in the United States more than 13 million people are infected each year and more than 65 million have an incurable STD. Generally, STD incidence has declined in the United States over the past 15 years, although rates among certain populations, including men who have sex with men, have increased.

Characteristics

Most STDs cause relatively harmless disease, producing few symptoms or no symptoms. However, some produce persistent asymptomatic or minimally symptomatic disease (e.g., chlamydia). Some people carry the disease for days or weeks, while others carry the disease for longer periods, even for life. During this time, an infected individual, or carrier, can spread disease.

In persistent infection, the pathogen evades detection by the immune system and remains fairly inactive, causing no overt disease. This inactivity is called latency. However, certain triggers (e.g., stress, immune suppression, injury) can reactivate latent pathogens. In some cases, reactivated disease is asymptomatic (e.g., chlamydia); in others, overt (e.g., genital herpes); and in still others, severe and even fatal (e.g., HIV/AIDS).

Complications of STD infection include pelvic inflammatory disease (PID) and cervicitis (inflammation of the cervix) in women, urethritis (inflammation of the urethra) and prostatitis (inflammation of the prostate) in men, and fertility and reproductive system problems in both sexes.

Possible consequences to a child infected by his or her mother, while in the womb or during birth, include stillbirth, blindness, and permanent neurological damage, depending on the disease.

A person infected with an STD is more likely to become infected with HIV, and a person infected with HIV and another STD is more likely to transmit HIV.

Treatment

Viral STDs, such as genital herpes (HSV) and human immunodeficiency virus (HIV), cannot be cured, but symptoms can be managed with medication. Bacterial STDs, such as gonorrhea and chlamydia, can be cured with antibiotics. Fungal (e.g., vaginal yeast infection) and parasitic (e.g., trichomoniasis) diseases can be cured with antifungal and antihelminthic agents, respectively. Early diagnosis and treatment increase the chances for cure.

Prevention

The only sure way to avoid becoming infected with an STD is monogamy with an uninfected partner. It is important for partners to discuss their sexual and STD history before having sex. Prevention is possible only if sexually active individuals understand STDs and how they are spread.

The risk for transmission is dramatically reduced with the use of condoms. The following behaviors and conditions can increase the risk for STDs:

• Engaging in sexual activity when either partner has unhealed lesions (e.g., genital herpes sores, genital warts)
• Enema or rectal douching before rectal intercourse
• Rectal or vaginal irritation or infection
• Sexual activity that may damage the mucosal lining of the vagina or rectum
• Tampon use (Tampons can cause vaginal dryness and cellular abnormalities. Sanitary napkins, either disposable or washable cotton pads, are recommended.)
• Vaginal dryness (Water-based lubricant is recommended.)