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STDs Today

Sexually transmitted diseases (STDs) affect men and women of all backgrounds and economic levels. In the United States, overall incidence of STDs has increased dramatically in recent years.1 The CDC estimates that 19 million new infections occur each year, almost half of them among young people ages 15 to 24.2

Despite the fact that STDs are extremely widespread and add an estimated $13 billion dollars to the nation's healthcare costs each year3, most people in the United States remain unaware of the risk and consequences of all but the most prominent STD—HIV, the virus that causes AIDS.

Common STDs and the Organisms That Cause Them
         Acquired Immune Deficiency Syndrome (AIDS)
         Genital Herpes/HSV
         Genital Warts/HPV
         Viral Hepatitis
         Other STDs
Who is Infected
         Variations in Risk
What Are Some Health Risks of STD Infection?
What is Being Done?

Common STDs and the Organisms That Cause Them

Many people are aware of the most prominent STD—HIV. However, many other STDs affect millions of men and women each year. Many of these STDs initially cause no symptoms, especially in women. Symptoms, when they do develop, may be confused with those of other diseases that are not transmitted through sexual contact. STDs can still be transmitted person to person even if they do not show symptoms. Also, health problems caused by STDs tend to be more severe for women than for men.

Below are descriptions of several of the most common STDs, including information about incidence, symptoms (if any), and treatment.

    Acquired Immune Deficiency Syndrome (AIDS)

    Acquired Immune Deficiency Syndrome (AIDS)AIDS (acquired immunodeficiency syndrome) was first reported in the United States in 1981. Since the beginning of the epidemic, an estimated 944,306 people have developed AIDS in the United States.4 AIDS is caused by the human immunodeficiency virus (HIV), a virus that destroys the body's ability to fight off infection.

    People who have AIDS are very susceptible to many life-threatening diseases, called opportunistic infections, and to certain forms of cancer. Transmission of the virus primarily occurs during unprotected sexual activity and by sharing needles used to inject intravenous drugs.

    Learn more about AIDS and HIV.


    ChancroidChancroid ("SHAN-kroid") is a bacterial infection caused by Haemophilus ducreyi, which is spread by sexual contact and results in genital ulcers. The disease is found primarily in developing and third world countries. Only a few hundred cases a year are diagnosed in the United States. The majority of individuals in the U.S. diagnosed with chancroid have traveled outside the country to areas where the disease is known to occur frequently.5

    The infection begins with the appearance of painful open sores on the genitals, sometimes accompanied by swollen, tender lymph nodes in the groin. These symptoms occur within a week after exposure. Symptoms in women are often less noticeable and may be limited to painful urination or defecation, painful intercourse, rectal bleeding, or vaginal discharge. Chancroid lesions may be difficult to distinguish from ulcers caused by genital herpes or syphilis. A physician must therefore diagnose the infection by excluding other diseases with similar symptoms. Chancroid is one of the genital ulcer diseases that may be associated with an increased risk of transmission of the human immunodeficiency virus (HIV), the cause of AIDS.

    People with chancroid can be treated effectively with one of several antibiotics.

    Learn more about chancroid infection. En Español.


    Chlamydia Chlamydial ("kla-MID-ee-uhl") infection is a common sexually transmitted disease (STD) caused by the bacterium, Chlamydia trachomatis. Chlamydia is the most frequently reported bacterial sexually transmitted disease in the United States. An estimated 2.8 million Americans are infected with chlamydia each year.6 Under-reporting is substantial because most people with chlamydia are not aware of their infections and do not seek testing. The highest rates of chlamydial infection are in 15- to 19-year-old adolescents, regardless of demographics or location.7 According to a 1997 report, the annual cost of chlamydial infection was estimated at over $2 billion.8

    Chlamydia can be transmitted during vaginal, oral, or anal sexual contact with an infected partner. A pregnant woman may pass the infection to her newborn during delivery, with subsequent neonatal eye infection or pneumonia. Even though symptoms of chlamydia are usually mild or absent, it can damage a woman's reproductive organs and cause serious complications. Irreversible damage, including infertility, can occur "silently" before a woman ever recognizes a problem. Chlamydia also can cause discharge from the penis of an infected man, although complications among men are rare.

    Pelvic inflammatory disease (PID), a serious complication of chlamydial infection, has emerged as a major cause of infertility among women of childbearing age.

    Chlamydia can be easily treated and cured with antibiotics.

    Learn more about chlamydial infection. En Español.

    Genital Herpes/HSV

    Genital Herpes/HSV Genital herpes is a contagious viral infection caused by the herpes simplex virus (HSV) which has affected an estimated one out of five (or 45 million) Americans. There are two types of HSV, and both can cause genital herpes. Genital HSV-2 infection is more common in women (approximately one out of four women) than in men (almost one out of five). Doctors estimate that as many as 500,000 new cases may occur each year.9

    HSV type 1 most commonly causes sores on the lips (known as fever blisters or cold sores), but it can cause genital infections through oral-genital or genital-genital contact. HSV type 2 most often causes genital sores, but it also can infect the mouth. Both HSV 1 and 2 can produce sores in and around the vaginal area, on the penis, around the anal opening, and on the buttocks or thighs. Occasionally, sores also appear on other parts of the body where broken skin has come into contact with HSV. The virus remains in certain nerve cells of the body for life, causing periodic symptoms in some people.

    Genital herpes infection usually is acquired by sexual contact with someone who unknowingly is having an asymptomatic outbreak of herpes sores in the genital area. People with oral herpes can transmit the infection to the genital area of a partner during oral-genital sex. Herpes infections also can be transmitted by a person who is infected with HSV who has noticeable symptoms. The virus is spread only rarely, if at all, by contact with objects such as a toilet seat or hot tub.

    There is no treatment that can cure herpes, but antiviral medications can shorten and prevent outbreaks during the period of time the person takes the medication.

    Learn more about genital herpes. En Español.

    Genital HPV Infection

    Genital Warts/HPV Human papillomavirus (HPV) is one of the most common causes of sexually transmitted disease (STD) in the world. Experts estimate that as many as 24 million Americans are infected with HPV, and the frequency of infection and disease appears to be increasing. At least 50 percent of sexually active men and women acquire genital HPV infection at some point in their lives. By age 50, at least 80 percent of women will have acquired genital HPV infection.10

    Human papillomavirus is the name of a group of viruses that includes more than 100 different strains or types. More than 30 of these viruses are sexually transmitted, and they can infect the genital area of men and women including the skin of the penis, vulva (area outside the vagina), or anus, and the linings of the vagina, cervix, or rectum. Low-risk types of HPV cause genital warts, the most recognizable sign of genital HPV infection. Other high-risk types of HPV cause cervical cancer and other genital cancers.11

    One study sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) reported that almost half of the women infected with HPV had no obvious symptoms. Because the viral infection persists, individuals may not be aware of their infection or the potential risk of transmission to others and of developing complications.12 Most people who become infected with HPV will not have any symptoms and will clear the infection on their own.

    There is no "cure" for HPV infection, although in most women the infection goes away on its own.

    In June 2006, the Advisory Committee on Immunization Practices (ACIP) voted to recommend the first vaccine developed to prevent cervical cancer and other diseases in females caused by certain types of genital human papillomavirus (HPV). The vaccine, Gardasil®, protects against four HPV types, which together cause 70% of cervical cancers and 90% of genital warts.13

    Learn more about genital warts and HPV. En Español.


    Gonorrhea Gonorrhea ( gone-or-REE-uh) is caused by Neisseria Gonorrhoeae, a bacterium that can grow and multiply easily in the warm, moist areas of the reproductive tract. CDC estimates that more than 700,000 persons in the U.S. get new gonorrheal infections each year. Only about half of these infections are reported to CDC.14

    The most common symptoms of infection are a discharge from the vagina or penis and painful or difficult urination. The most common and serious complications occur in women and, as with chlamydial infection, these complications include Pelvic Inflammatory Disease (PID), ectopic pregnancy, and infertility.

    Gonorrhea can grow in the cervix (opening to the womb), uterus (womb), and fallopian tubes (egg canals) in women, and in the urethra (urine canal) in women and men. The bacterium can also grow in the mouth, throat, eyes, and anus. If it spreads to the blood or joints it can be life-threatening. In addition, people with gonorrhea can more easily contract HIV, the virus that causes AIDS. HIV-infected people with gonorrhea are more likely to transmit HIV to someone else.

    Several antibiotics can successfully cure gonorrhea in adolescents and adults. However, drug-resistant strains of gonorrhea are increasing in many areas of the world, including the United States, and successful treatment of gonorrhea is becoming more difficult. New antibiotics or combinations of drugs must be used to treat these resistant strains.

    Learn more about gonorrhea. En Español.


    Syphilis Syphilis (SIF·i·lis) is caused by the bacterium Treponema Pallidum. The incidence of syphilis has increased and decreased dramatically in recent years, and in the United States, health officials reported over 32,000 cases of syphilis in 2002. Between 2001 and 2002, the number of reported primary and secondary (P & S) syphilis cases increased 12.4 percent. Rates in women continued to decrease, and overall, the rate in men was 3.5 times that in women. This, in conjunction with reports of syphilis outbreaks in men who have sex with men (MSM), suggests that rates of syphilis in MSM are increasing.15

    Syphilis is passed from person to person through direct contact with a syphilis sore. The first symptoms of syphilis infection may go undetected because they are very mild and disappear spontaneously. The initial symptom is a chancre (genital sore); it is usually a painless open sore that most often appears on the penis or around or in the vagina. It can also occur near the mouth, anus, or on the hands. Transmission of the organism occurs during vaginal, anal, or oral sex. Pregnant women with the disease can pass it to the babies they are carrying.

    If untreated, syphilis may go on to more advanced stages, including a transient rash and, eventually, can cause serious involvement of the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. Chancres caused by syphilis make it easier to transmit and acquire HIV infection sexually. There is an estimated 2- to 5-fold increased risk of acquiring HIV infection when syphilis is present.16 The full course of the disease can take years.

    Penicillin remains the most effective drug to treat people with syphilis.

    Learn more about syphilis. En Español.


    Trichomoniasis (trick-oh-moe-NYE-uh-sis) is caused by the single-celled protozoan parasite, Trichomonas vaginalis. It is the most common curable STD in young, sexually active women, and it affects men as well although symptoms are most common in women. An estimated 7.4 million new cases occur each year.17

    The vagina is the most common site of infection in women, and the urethra (urine canal) is the most common site of infection in men. The parasite is sexually transmitted through penis-to-vagina intercourse or vulva-to-vulva (the genital area outside the vagina) contact with an infected partner. Women can acquire the disease from infected men or women, but men usually contract it only from infected women.

    Most men with trichomoniasis do not have signs or symptoms; however, some men may temporarily have an irritation inside the penis, mild discharge, or slight burning after urination or ejaculation. Some women have signs or symptoms of infection which include a frothy, yellow-green vaginal discharge with a strong odor. The infection also may cause discomfort during intercourse and urination, as well as irritation and itching of the female genital area.

    Trichomoniasis can usually be cured with the prescription drug, metronidazole, given by mouth in a single dose.

    Learn more about trichomoniasis. En Español.

    Viral Hepatitis

      Hepatitis A is a liver disease caused by the hepatitis A virus (HAV). Hepatitis A virus is spread from person to person by putting something in the mouth that has been contaminated with the stool of a person with hepatitis A.  This type of transmission is called "fecal-oral." Fewer than 5 percent of infections are transmitted through fecal-oral contact during sexual intercourse. Two products are used to prevent hepatitis A virus infection: immune globulin and hepatitis A vaccine.

      Hepatitis B Hepatitis B is a serious disease caused by a virus that attacks the liver. The virus, which is called hepatitis B virus (HBV), can cause lifelong infection, cirrhosis (scarring) of the liver, liver cancer, liver failure, and death. HBV is spread when blood from an infected person enters the body of a person who is not infected. For example, HBV is spread through having sex with an infected person without using a condom (the efficacy of latex condoms in preventing infection with HBV is unknown, but their proper use might reduce transmission), by sharing drugs, needles, or "works" when "shooting" drugs, through needlesticks or sharps exposures on the job, or from an infected mother to her baby during birth. Of approximately 200,000 new HBV infections in the United States each year, approximately half are transmitted through sexual intercourse. Preliminary data from a large U.S. multisite study indicate that approximately one third of persons with acute hepatitis B virus infections in 1995 had a history of another STD.18

      Hepatitis C is a liver disease caused by the hepatitis C virus (HCV). HCV is spread primarily by direct contact with human blood, including sharing of needles for injection drug use and sex with someone with HCV. There is no vaccine to prevent hepatitis C .

      Hepatitis D (delta) is a liver disease caused by the hepatitis D virus (HDV), a defective virus that needs the hepatitis B virus to exist. Hepatitis D virus (HDV) is found in the blood of persons infected with the virus. Infection occurs when blood from an infected person enters the body of a person who is not immune. Hepatitis B vaccine should be given to prevent HBV/HDV co-infection.

      Hepatitis E is a liver disease caused by the hepatitis E virus (HEV) transmitted in much the same way as hepatitis A virus. Hepatitis E, however, does not occur often in the United States. HEV is found in the stool (feces) of persons and animals with hepatitis E and spread by eating or drinking contaminated food or water.

      At present, there are no specific treatments for the acute symptoms of viral hepatitis. Doctors recommend bed rest, a healthy diet, and avoidance of alcoholic beverages. A genetically engineered form of a naturally occurring protein, interferon alpha, is used to treat people with chronic hepatitis C. Studies supported by the National Institutes of Health led to the approval of interferon alpha for the treatment of those with chronic HBV as well.

    Learn more about viral hepatitis.

    Other STDs

    Other diseases that may be sexually transmitted include bacterial vaginosis, scabies, pubic lice, and Pelvic Inflammatory Disease (PID). For more information, visit the National Institute of Allergy and Infectious Diseases, Sexually Transmitted Infections Web page .

Who is Being Infected?

In the United States alone, an estimated 19 million new cases of STDs are reported each year.19 This table shows the incidence and prevalence of some of the most common STDs.

STD Incidence * Prevalence **
Chlamydia 2,800,00020 ***
Gonorrhea 700,00021 ***
Syphilis 32,00022 (reported) ***
Herpes (HSV) 1,000,00023 45,000,00024
Hepatitis B (HBV) 60,00025 1,250,00026
Genital Warts / Human Papillomavirus (HPV) 6,200,00027 20,000,00028
Trichomoniasis 7,400,00029 ***

* Estimated number of new cases each year
** Estimated number of people currently infected
*** No recent surveys on national prevalence for gonorrhea, syphilis, or trichomoniasis have been conducted.

    Variations in risk

    STDs affect men and women of all backgrounds and economic levels. However, STDs disproportionately affect women, infants of infected mothers, adolescents and young adults, and communities of color. Although 15-24-year-olds represent only one-quarter of the sexually active population, they account for nearly half of all new STDs each year.30

    Some contributing factors in the rise of STDs, particularly among young people, are that teenagers are increasingly likely to have more sex partners at earlier ages, and sexually active teenagers often are reluctant to obtain STD services, or they may face serious obstacles when trying to obtain them. In addition, health care providers often are uncomfortable discussing sexuality and risk reduction with their patients, thus missing opportunities to counsel and screen young people for STDs.31

    For more information on at-risk populations, visit the Communities at Risk section of this Website.

What Are Some Health Risks of STD Infection?

STDs can result in irreparable lifetime damage, including blindness, bone deformities, mental retardation, and death for infants infected by their mothers during gestation or birth.

In women, STDs can lead to pelvic inflammatory disease (PID), infertility, potentially fatal ectopic pregnancies, and cancer of the reproductive tract.

What Is Being Done?

Prevention—both biomedical and behavioral—is the best hope for reducing or eliminating STDs.

As the lead agency for STD prevention in the United States, CDC is tasked with providing national leadership through research, policy development, and support of effective services to prevent STDs (including HIV infection) and their complications, such as enhanced HIV transmission, infertility, adverse outcomes of pregnancy, and reproductive tract cancer. The Division of STD Prevention, part of CDC's National Center for HIV, Viral Hepatitis, STD, and TB Prevention, coordinates CDC's STD prevention efforts.

1 State of the Nation Report 2005: Challenges Facing STD Prevention in Youth
American Social Health Association.
2 Weinstock H, Berman S, Cates W. Sexually transmitted diseases among American youth: incidence and prevalence estimates, 2000. Perspectives on Sexual and Reproductive Health 2004;36(1):6-10, cited in CDC Trends in Reportable Sexually Transmitted Diseases in the United States, 2004.
3 HW Chesson, JM Blandford, TL Gift, G Tao, KL Irwin. The estimated direct medical cost of STDs among American youth, 2000. Abstract P075. 2004 National STD Prevention Conference. Philadelphia, PA. March 8-11, 2004, cited in CDC Trends in Reportable Sexually Transmitted Diseases in the United States, 2004.
4 Basic Statistics from HIV/AIDS Surveillance Report, 2004. Vol. 16. Atlanta: US Department of Health and Human Services, Centers for Disease Control and Prevention; 2005.
5 Chancroid, Medline Plus, U.S. National Library of Medicine, and the National Institutes of Health.
6 Chlamydia, CDC.
7 Healthy People 2010, Sexually Transmitted Diseases.
8 CDC Media Release.
9 Genital Herpes, CDC.
10 Genital HPV Infection, CDC.
11 Genital HPV Infection, CDC.
12 Human Papillomavirus and Genital Warts, National Institute of Allergy and Infectious Diseases (NIAID).
13 HPV Vaccine Questions and Answers, CDC.
14 Gonorrhea, CDC.
15 Syphilis, CDC.
16 Syphilis, CDC.
17 Trichomoniasis, CDC.
18 Alter and Mast, 1994; CDC, 1994b; Goldstein et al., 1996, cited in The Hidden Epidemic: Confronting Sexually Transmitted Diseases (1997), Institute of Medicine (IOM).
19 Trends in Reportable Sexually Transmitted Diseases in the United States, 2004, CDC.
20 Weinstock H, Berman S, Cates W. Sexually transmitted diseases among American youth: incidence and prevalence estimates, 2000. Perspectives on Sexual and Reproductive Health 2004;36(1):6-10, cited in CDC Trends in Reportable Sexually Transmitted Diseases in the United States, 2004.
21 Gonorrhea, CDC.
22 Syphilis, CDC.
23 Tracking the Hidden Epidemics 2000.
24 Genital Herpes, CDC.
25 Viral Hepatitis B Fact Sheet, CDC.
26 Viral Hepatitis B Fact Sheet, CDC.
27 Genital HPV Infection, CDC.
28 Genital HPV Infection, CDC.
29 Trichomoniasis, CDC.
30 Weinstock H et al., Sexually transmitted diseases among American youth: incidence and prevalence estimates, 2000, Perspectives on Sexual and Reproductive Health, 2004, 36(1):6–10, cited in Guttmacher Institute Facts on American Teens' Sexual and Reproductive Health.
31 Healthy People 2010, Sexually Transmitted Diseases.

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