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Mailman School of Public Health

The Harriet and Robert Heilbrunn Department of Population and Family Health

intro | reproductive anatomy and physiology | contraception | pregnancy, childbirth and lactation
| maternal mortality | sexually transmitted infections

Sexually Transmitted Infections

Table of Contents

Common Sexually Transmitted Infections
Other Genital Tract/Reproductive Tract Infections
Prevention of Sexually Transmitted Infection


Sexually transmitted infections (STIs) have historically been referred to as venereal disease, named for Venus, the goddess of love. Medical providers and public health practitioners today have replaced this term with more accurate and neutral terminology: sexually transmitted disease (STD) or sexually transmitted infection (STI).

The term reproductive tract infection (RTI) is often used to describe infections that are sexually transmitted, as well as other common infections that may or may not be sexually transmitted (i.e. candidiasis, bacterial vaginosis).

Epidemiology of STIs

  • Sexually transmitted infections (STI's) are transmitted from person to person through vaginal, oral, or anal sex with an infected partner; and/or from a pregnant woman (if infected) to her fetus or baby during pregnancy and labor and delivery.
  • In 2008, the CDC reported that a nationally representative study estimated that 1 in 4 teenage girls in the U.S. has an STD.  The study included the most common STDs: HPV, chlamydia, herpes simplex virus, and trichomoniasis.
  • There are approximately 15 million new cases of sexually transmitted infection each year in the United States, and 340 million worldwide.30
  • The majority of STI's are asymptomatic (no symptoms). Asymptomatic infections can be transmitted to sexual partners.
  • Having certain sexually transmitted infections increases the risk of acquiring or transmitting HIV.

Gender Disparities

Although the health risks associated with STIs affect both women and men, women are disproportionately affected. Women are more likely then are men to have asymptomatic infections, and also have greater biological susceptibility to acquire infections if exposed.

Untreated STIs in women can lead to pelvic inflammatory disease (PID), infertility, ectopic pregnancy, cancers of the reproductive tract, pregnancy loss, neonatal morbidity and mortality, and an increased risk of HIV transmission.

Untreated STIs in men can lead to an increased risk of HIV transmission, prostatitis, epididymitis, infertility, and reactive arthritis (formerly known as Reiter’s syndrome).

Common Sexually Transmitted Infections

There are over 20 different sexually transmitted infections, and other infections that are considered “sexually associated”. Viruses, and bacteria cause the majority of STIs. Bacterial STIs, which include infections such as chlamydia, gonorrhea, and syphilis, can be cured with antibiotics. Viral STIs, including HPV, herpes, hepatitis, and HIV, cannot be cured, though they can often be treated. The most common STIs are discussed below.

Bacterial STIs:

It is important to note that all bacterial STIs can be prevented by correct and consistent condom use.


  • Caused by the bacteria Chlamydia trachomatis.
  • Currently, the most commonly reported infectious disease in the United States as well as the leading cause of infertility and ectopic pregnancy.
  • Chlamydia is predominantly asymptomatic in both women and men. If symptoms do occur, they include abnormal discharge, burning with urination, and abdominal pain.
  • Uncomplicated chlamydia can be effectively treated with antibiotics. Partner treatment and risk reduction education (e.g. about condom use) are needed to reduce the risk of re-infection.
  • Undetected and untreated chlamydia can result in pelvic inflammatory disease, infertility, and ectopic pregnancy in women; neonatal pneumonia and conjunctivitis in newborns; and epididymitis, (a painful condition of the testes that can lead to infertility if left untreated), prostatitis, urethritis, and reactive arthritis in men.
  • The current recommendation is that sexually active women younger than 25 years of age be screened for chlamydia annually, particularly because up to 90% of women with chlamydia are asymptomatic. (USPTF website).

Gonorrhea (GC)

  • Caused by the a bacteria Neisseria gonorrhoeae
  • Grows in the genital tract of both men and women, and can also be found in the mouth, the eyes, the throat and the anus.
  • The majority of people with GC have no symptoms or mild symptoms that can be easily missed. If present symptoms include vaginal or penile discharge, and/or painful urination.
  • Complications related to untreated GC for women include PID, ectopic pregnancy, and infertility.
  • Men with untreated GC can develop epididymitis.
  • Can result in neonatal blindness, and life-threatening infections in the newborn.
  • For both men and women, untreated gonorrhea can spread to the blood and joint and become life-threatening.
  • Uncomplicated GC can be effectively treated with antibiotics.
  • Antibiotic resistance to GC has become prevalent, therefore follow-up within 2-3 weeks of treatment is recommended to ensure that the infection has been cured.


Syphilis is a multi-phase infection caused by the bacteria Treponema pallidum.

The three phases of infection are described below:

  • Primary – characterized by the appearance of a painless genital ulcer which lasts about 3-6 weeks and usually resolves on its own. Resolution of the ulcer does not represent resolution of the infection however. If untreated in primary stage, syphilis will progress to the secondary stage.
  • Secondary characterized by a rash anywhere on the body, condylomata lata (fleshy, moist tissue growth), alopecia (hair loss), and/or lymphadenopathy (swollen glands) and fever. If untreated, secondary syphilis will become latent.
  • Latent - begins when the secondary symptoms resolve, and for many years there may be no evidence of infection. If untreated can result in neurosyphilis (multiple signs and symptoms of neurological impairment), cardiovascular syphilis (aortic aneurism, aortic insufficiency), bone and joint involvement, and death.

Congenital (present at birth) syphilis can result in stillbirth, developmental delays, and/or death. A simple blood test is available to screen for syphilis and should be a routine component of preventive health screening, including prenatal care. If detected in early stages, syphilis is easily treated with antibiotics.

For more information on syphilis visit:


  • Caused by the bacteria Haemophilus ducreyi.
  • Genital ulcer disease characterized by painful sores on genital organs that may be difficult to distinguish from lesions associated with syphilis or herpes.
  • Women more likely than men to have mild or unnoticeable symptoms.
  • Rare in the United States and more common globally (i.e. sub-Saharan Africa).
  • Effectively treated with antibiotics
  • Associated with increased risk of HIV transmission.

Viral STIs

Human Papillomavirus (HPV)

  • There are more than strains of the human papillomavirus.
  • Most HPV is asymptomatic.
  • HPV usually causes genital warts called condyloma acuminata (small hard and painless bumps). Warts can be removed by chemical or surgical treatment..
  • HPV can also cause sub-clinical genital HPV (HPV infection in the absence of genital warts) that is usually detected by the Pap smear. In addition to the Pap test, direct testing for HPV is now available..
  • Certain HPV types (16, 18, 33, and 35) have been strongly associated with cancer of the cervix.
  • Treatment for sub-clinical HPV depends on a variety of factors, which include the type of HPV, the age of the patient, and the extent of the cervical changes.
  • Correct and consistent use of condoms reduces the risk of transmitting HPV, but does not eliminate it, as HPV can be passed through sexual contact with areas not covered by a condom, even without intercourse.
  • In 2006, the FDA approved Gardasil, a vaccine that protects against 4 strains of HPV (6, 11, 16 and 18).
  • Gardasil is offered in a series of three injections over a six month period—dose 1, followed by a second dose 2 months later and a third dose 6 months after dose 1. Currently the vaccine is only approved for girls and women from 9-26 years of age, though it is recommended that girls be vaccinated at the age of 11 or 12 years old, before they become sexually active. Each dose costs around $120, with varying insurance coverage. Merck does offer financial assistance to some women through the Merck Vaccine Patient Assistance Program. Note that the vaccine cannot be used as a treatment for HPV.

Herpes (HSV) (Herpes Simplex Virus).

  • Genital ulcer infection caused by the HSV. There are two types: HSV-1 and HSV-2. Most cases of genital herpes are caused by HSV-2.
  • Approximately 200,000 people (1 in 5 adults) have a primary outbreak of or are affected by symptomatic herpes each year, and approximately 45 million Americans are infected.
  • Causes painful genital ulcers.
  • In most cases, herpes is transmitted by people who are unaware they are infected.
  • Correct and consistent use of condoms reduces the risk of transmitting HSV, but does not eliminate it, as herpes can be passed through sexual contact with areas not covered by a condom, even without intercourse.
  • Antiviral treatments help to decrease the symptoms and shorten or prevent outbreaks, but they do not “cure” the infection. Currently, Valtrex® is the primary medication prescribed to reduce duration and discomfort of herpes symptoms.
  • If active herpes infection is present near the time of delivery, a pregnant woman can transmit the virus to her baby during a vaginal delivery. Cesarean-sections are usually recommended if active infection is present.
  • Herpes may increase the risk of HIV transmission.


  • Three types: HAV (Hepatitis A), HPB (Hepatitis B) and HPC (Hepatitis C).
  • Hepatitis A primarily transmitted through feces-contaminated food and water, but can also be transmitted sexually particularly through oral-anal contact
    • Thorough cleaning of the genitals and anus before sexual activity reduce the likelihood of transmitting Hepatitis A. The use of a barrier method (such as a dental dam or condom) during sex, particularly anal sex and oral-anal contact will also reduce the risk of transmission.
  • Hepatitis B primarily transmitted by having unprotected oral, anal, or vaginal sex, but also transmitted through exposure to blood and blood products.
    • The correct and consistent use of condoms greatly reduces the risk of Hepatitis B transmission.
  • Hepatitis C primarily transmitted through exposure to blood and blood products and is rarely transmitted sexually.
    • The correct and consistent use of condoms greatly reduces the risk of Hepatitis C transmission.
  • Hepatitis A, B, and C, can all be asymptomatic, but can also cause acute and chronic liver disease.
  • Vaccinations are available to prevent Hepatitis A and Hepatitis B. These vaccines are covered by many insurance policies or made available at low-cost through vaccine programs. No vaccine available for the prevention of Hepatitis C.
    • The Hepatitis A vaccine is offered as a 2-injection series, with the doses given 6 to 18 months apart. This vaccine is recommended for specific higher risk populations. For more information, see:
    • The Hepatitis B vaccine is a series of 3 injections over a six month period. It is recommended for all people ages 0-18, as well as high-risk adult populations.


  • HIV, (Human Immune Deficiency Virus) is a viral infection that attacks the T cells (also called CD4cells). T cells are lymphocytes (white blood cells) that trigger the body's immune response to infection. When the number of CD4 cells decrease, so does the body's ability to fight infection.
  • HIV is the virus that causes AIDS (Acquired Immunodeficiency Syndrome), which is diagnosed when an HIV-positive individual’s CD4 cell count falls below 200. Blood tests that measure CD4 counts are used to monitor immune status and response to anti-retroviral medications.
  • Disease progression from HIV to AIDS varies (from a few months to 17 years with the median begin 10 years without treatment32. Anti-retroviral medications can slow the decline of the immune system, and research and development of new drugs is on-going.
  • HIV is transmitted in vaginal fluids, semen, blood, and breast milk.
  • Behaviors that transmit these fluids are vaginal, oral, and anal sex; injection drug use; other behaviors that put individuals in contact with blood products or equipment (i.e. needle sharing, tattooing, body piercing); and through pregnancy, childbirth, and/or breast-feeding.
  • Correct and consistent condom use is very effective at preventing the transmission of HIV.
  • More recently, clinical trials in various African countries show that male circumcision also confers some protection to men against the contraction of HIV, though condoms should still be used during sexual intercourse for better protection.
  • HIV counseling and testing is the standard of care for anyone who is sexually active as well as for pregnant women.
  • Having an STI increases the risk of acquiring HIV by 2-5 times.  

Babies born to HIV-positive pregnant women will all have positive HIV tests, even though only 25% of these babies are likely to be infected (if left untreated). Babies are born with their mother's antibodies and the HIV test determines whether the HIV antibody, and not the virus itself, is present. If the baby is not infected with HIV, the antibody status will revert to negative status as the baby develops its own immune system during the first year. Anti-retroviral medications and other treatments during pregnancy and labor reduce the risk of maternal HIV transmission to as little as 2%.33

Other Genital Tract/Reproductive Tract Infections


  • Caused by genital tract protozoan Trichomonas vaginales.
  • Infection occurs in both men and women, though symptoms are more common in women.
  • About half of trichomoniasis infections are asymptomatic. If symptoms are present they include: frothy greenish-yellow vaginal discharge with a strong odor and/or vaginal itching and inflammation.
  • Untreated infection in pregnant women is associated with an increased risk of low birth weight and premature birth.
  • Diagnosed by wet mount (examination of vaginal fluids microscopically).
  • Treated with Metronidazole.
  • Correct and consistent condom use reduces the risk of transmission.

Vaginal Yeast Infection

  • Caused by fungus Candida albicans.
  • Usually not a sexually transmitted infection
  • Yeast infections are asymptomatic in about 10-15% of women. If there are symptoms they include inflammation, vaginal itching or discomfort, and/or white thick discharge.
  • Increased incidence among women during pregnancy, diabetes, or following antibiotic administration.

Bacterial Vaginosis (BV)

  • Disruption of normal vaginal flora when lactobacillus is replaced by other vaginal bacteria (i.e. gardnerella, mycoplasma hominis, and various anaerobic bacteria).
  • Considered a “sexually associated” condition, but not considered a specific STI.
  • Male treatment not proven to be effective in preventing recurrence.
  • Vaginal itching and inflammation are common symptoms but asymptomatic infection is common. Treatment is recommended only for women with symptoms.
  • BV associated with an increased risk of pre-term labor and low birth weight.34

Prevention of Sexually Transmitted Infection

In 2003, The World Health Organization (WHO) conceptualized the prevention and control of STIs as a “public health package” consisting of the following components:

  • The promotion of safer sexual behavior
  • Condom programming—encompassing a full range of activities from condom promotion to the planning and management of supplies and distribution
  • Promotion of health care-seeking behavior
  • Integration of STI prevention and care into primary health care
  • The provision of specific services for populations at risk—such as female and male sex workers, adolescents, long-distance truck drivers, military personnel and prisoners—by health care facilities, private clinics, and other service providers.
  • Comprehensive case management of STIs
  • Prevention and care of congenital syphilis and neonatal conjunctivitis
  • Early detection of symptomatic and asymptomatic infections36

Similarly, the 2002 CDC Clinical Prevention Guidelines base the prevention and control of STDs on the following five major concepts:

  • Education and counseling of persons at risk on ways to adopt safer sexual behavior,
  • Identification of asymptomatically infected persons and of symptomatic person unlikely to seek diagnostic and treatment services,
  • Effective diagnosis and treatment of infected persons,
  • Evaluation, treatment, and counseling of sex partners of persons who are infected with an STD
  • Pre-exposure vaccination of persons at risk for vaccine-preventable STDs.37

The STI Syndromic Approach, is one example of a strategy specifically designed to address STI infection in areas of the world where resources are scarce, laboratory testing is not readily available, and rates of STI and HIV are high. Syndromic management involves the treatment of signs and symptoms using an algorithm of decision points to treat symptoms (i.e. vaginal discharge, urethral discharge, genital ulcers and pelvic pain), rather than laboratory tests. Although the identification of cervical infections such as gonorrhea and chlamydia are not highly effective with this method, use of the method resulted in a 42% reduction of HIV transmission in Tanzania.38


For more information:

CDC Program Guidelines for STD Prevention

American Social Health Association

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