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Sexually Transmitted Diseases (STDs)

  • Infectious diseases that spread from person to person through vaginal, anal, or oral sex
  • Some of the types are HIV, HPV, chlamydia, gonorrhea, syphilis, genital herpes, trichomoniasis
  • Treatment depends on the cause of infection, and can include antibiotics or antiviral drugs
  • Involves infectious diseases, gynecologic specialties, AIDS care program, urology

Sexually Transmitted Diseases (STDs)


Sexually transmitted diseases (STDs) might be difficult to talk about, but it’s important to realize the risks they pose and how common they are. The total combined cases of reported chlamydia, gonorrhea and syphilis reached the highest number ever in the United States in 2018.

The increase in those three STDs, also called sexually transmitted infections, or STIs, is affecting teens and young adults the most. More than half of gonorrhea and chlamydia cases are in people under the age of 25, and nearly one in four teenage girls has an STD.

“What’s often not understood is that many of these STDs can have long-term consequences, especially for women,” says Sangini S. Sheth, MD, MPH, a Yale Medicine obstetrician-gynecologist. Having had an STD puts a woman at higher risk for a wide range of conditions, including pelvic pain, fertility problems and increased risk of ectopic pregnancies (when the fertilized egg implants outside the uterus). For men, STDs raise the risk for lifelong infections, infertility and possibly cancer. 

Since many STDs have no symptoms, people can unknowingly spread infections to their sexual partners. At Yale Medicine, we diagnose and treat women, men and young adults with STDs, and our physicians are involved in numerous research projects related to improving protection from various STDs.

What are sexually transmitted diseases (STDs)?

Sexually transmitted diseases (STDs) are infectious diseases that spread from person to person through vaginal, anal and oral sex. They are caused by bacteria, parasites and viruses.

Common STDs include:

  • HIV: Human immunodeficiency virus, or HIV, attacks the immune system, which is your natural defense against illness. HIV causes AIDS, or acquired immune deficiency syndrome. Early on, there may be no signs or symptoms. If and when a person with HIV becomes sick with associated infections, they are said to have AIDS.
  • HPV: Human papillomavirus (HPV) is a group of more than 150 related viruses. Each gets its own number, called its HPV type. Many forms of HPV cause warts (papillomas) often found on the inside or outside of the genitals. Genital warts can spread to surrounding skin or to a sexual partner. Some HPV types have no symptoms and vanish without ever causing health problems. However, if the virus lasts, it can lead to abnormal changes in the cells, which can progress to cervical cancer. 
  • Chlamydia: This STD is caused by bacteria called chlamydia trachomatis. Women get the infection in their cervix, rectum or throat. Men can get it in their urethra, rectum or throat. It can cause abnormal genital discharge and burning during urination. In women, chlamydia can lead to pelvic inflammatory disease (an infection in the uterus, ovaries or fallopian tubes), tubal (ectopic) pregnancies and infertility. If passed on to a baby, it can cause eye infections or pneumonia. Chlamydia testing is important because it’s treatable with antibiotics; since it doesn’t always bring symptoms, many people with chlamydia don’t know they have it.
  • Gonorrhea: Easily treated with antibiotics, this bacterial infection is carried in semen and vaginal fluids. Symptoms include burning, itching, redness and swelling in the vagina or penis as well as frequent urination. Left untreated, it can cause pelvic inflammatory disease, tubal pregnancy and infertility, and joint infection and arthritis (known as disseminated gonococcal infection). Gonorrhea can also be spread during childbirth and cause serious eye infections to babies.
  • Genital herpes: This condition is caused by the herpes simplex virus (HSV) and usually appears as one or more blisters on or around the genitals, rectum or mouth. When the blisters pop, they leave painful sores, which may take weeks to heal. There is no cure for HSV. The virus stays in the body, and the sores may return. Medicine can shorten an outbreak or help with symptoms. The virus is spread during sexual intercourse or from the mouth to the genitals during oral sex, even when a person has no visible blisters. It can also be spread to babies during childbirth.
  • Syphilis: This STD shows up as a painless open sore on the penis, in the vagina or on the skin around either organ. Left untreated, it proceeds to a rash and then causes problems with the heart and central nervous system. The disease can be treated with antibiotics, though treatment might not reverse any damage that was already done. For a pregnant woman, syphilis can be dangerous for her baby.
  • Trichomoniasis: Also known as “trich,” this is a parasitic infection that spreads during sex. Symptoms can vary (but usually take the form of genital irritation) and only arise in about 30 percent of people who have it. In women, it most commonly affects the vulva, vagina, cervix or urethra. In men, it most commonly affects the inside of the penis, which is called the urethra. 

Though HIV does not always develop into AIDS, it can be passed on during sexual activity and by sharing needles used to inject drugs. It can also be passed on to a baby during pregnancy, delivery and breastfeeding. Although neither HIV nor AIDS can be cured, thanks to new medical treatments people with the disease are living longer than ever.

Women with infections from certain types of HPV have an increased risk of getting cervical cancer. To check for HPV infection, doctors offer a high-risk HPV test. A Pap test (or smear), which can be done at the same time, can identify abnormal cervical cells, which can be a precursor to cancer.An HPV vaccine, now recommended for girls and boys age 9 to 26, protects against the types of HPV that cause most cervical cancers.

What are the symptoms of STDs?

STDs can have a wide array of signs and symptoms—and sometimes none at all. As a result, an infection might progress unnoticed until serious problems develop and/or a sexual partner is infected. Symptoms can arise within days of exposure or years later.

Signs and symptoms that might indicate an STD include:

  • Sores or bumps in, on or around the genitals or in the mouth or rectal area
  • Rash, especially over the torso, hands or feet
  • Burning or painful urination
  • Unusual vaginal bleeding
  • Discharge from the penis
  • Unusual or strange smelling vaginal discharge
  • Pain during sex
  • Lower abdominal pain
  • Fever

STDs can cause long-term harm, including chronic pain and infertility. Each year, untreated STDs cause infertility in at least 24,000 women in the U.S., the CDC reports. Untreated syphilis in pregnant women causes infant death in up to 40 percent of cases. 

What are the risk factors for STDs?

If you are sexually active, you are at risk for developing an STD. These factors can increase your risk:

  • Unprotected sex: Having vaginal or anal sex without a latex condom dramatically increases your risk. Using condoms inconsistently or improperly also raises your odds of getting an STD.
  • Injecting drugs: Needle sharing can spread STDs as well as infections, including hepatitis B and C.
  • Multiple partners: Having multiple partners increases your chance of contracting an STD.
  • Personal history: Already having one STD, especially an active one, makes it easier for another to take hold, including HIV.  
  • Age: Nearly half of all STD cases in the United States occur in people under the age of 25.
  • Men who have sex with men: Compared to other groups, men who have sex with men are at a higher risk of getting an STD. 

How are STDs detected?

Laboratory tests can confirm an STD and identify other infections. Tests include:

  • Blood tests: These can confirm HIV and later stages of syphilis.
  • Urine: Samples can show gonorrhea, chlamydia and trichomoniasis. One test allows providers to check for all three diseases at once. “For gonorrhea and chlamydia, we use a DNA-based test, which is highly accurate,” Dr. Sheth says.
  • Fluid: Samples of fluid and tissue from active sores are used to diagnose genital herpes. 

What routine screenings are recommended for STDs?

Screenings are often recommended for the following STDs:

  • Chlamydia and gonorrhea: At Yale Medicine, we follow guidelines from the American College of Obstetricians and Gynecologists and from the U.S. Preventive Services Task Force, which recommend women under age 25 get screened annually for chlamydia and gonorrhea. Older women who are at increased risk should also be screened. Routine screenings aren’t currently recommended for men, partly because evidence shows their infections are more likely to cause symptoms that lead to diagnosis and treatment. At the moment, studies have not properly shown that screening men reduces disease transmission in women.

If you have any suspicion that you might have been exposed to or actually have an STD, see a doctor for testing. “We get a lot of patients who come in and want to be tested because they have a new partner or they might have been exposed or they are having symptoms,” Dr. Sheth says. “If they have one STD, we recommend testing for everything else as many of them, including chlamydia and gonorrhea, travel together.”

  • HPV: We follow American Cancer Society recommendations that women between ages 30 and 65 receive an HPV test along with a Pap smear (called a co-test) every five years. Both tests can be done with the same cervical Pap brush specimen and checks for cervical cancers and pre-cancers.
  • HIV: The CDC recommends everyone between ages 13 and 64 get tested for HIV at least once, as part of their routine health care. All pregnant women should also be tested. 

HPV is so common in women under age 30 that routine HPV testing is not recommended for this group. “We might pick up a transient infection that, in a normal, healthy person, the body will likely take care of it on its own,” Dr. Sheth explains. “But an important message is that 50 percent of cervical cancer is diagnosed in women who have been under-screened, meaning they haven’t had a Pap smear in the last five years.”

Women between the ages of 21 and 29 should have Pap tests every three years, and HPV testing is recommended for those who receive abnormal Pap test results.

HPV testing still has a long way to go. Though the virus can be found in the mouth or throat, there are no FDA-approved tests to identify the virus in these locations. And, as of yet, there is no FDA-approved HPV test for men.

How are STDs treated?

Appropriate treatment for STDs varies depending on the cause of the infection. For pregnant women, prompt treatment can prevent or reduce the risk of infection spreading to your baby. Options include:

  • Antibiotics: These are used to treat STDs from bacteria or parasites. This category includes gonorrhea, syphilis, chlamydia and trichomoniasis. Most of the medicines are oral, though an intramuscular injection is used for gonorrhea, which has a growing problem of antibiotic resistance, Dr. Sheth says.
  • Antiviral drugs: Viral infections can’t always be cured, but they can be managed with antiviral drugs.

For HIV, antiviral drugs can control the virus and allow people to live longer, healthier lives. They also reduce, but do not eliminate, the risk of spreading the virus to others.

For herpes, you will have fewer recurrences if you take an antiviral drug daily. The medications lessen the risk of spreading infection, but it is still possible to spread herpes to a partner.

“For herpes and HIV, we can suppress the viruses with antiviral medications, but we can’t cure them,” Dr. Sheth says. 

Is there a way to protect a sexual partner from an STD?

The only way to avoid spreading an STD is to not have vaginal, anal or oral sex. If you remain sexually active you can lower the chances of spreading an STD if you:

  • Share your test results with your partner. In Connecticut, as well as in 38 other states, physicians can write a prescription for a patient’s partner for treatment of gonorrhea or chlamydia. This is called expedited partner therapy. “A lot of research shows this is hugely beneficial in getting people treated,” Dr. Sheth says.
  • Get the HPV vaccine. It is FDA-approved for ages 9 through 26. It is effective for preventing many strains of HPV if it is administered before you become sexually active, but it also offers some protection for those who already started engaging in sex.
  • Be monogamous.
  • Reduce your number of sex partners. 
  • For vaginal, anal or oral sex, use a latex condom, a female condom or a dental dam (a piece of rubber used to cover the genitals during oral sex). 

What makes Yale Medicine stand out when it comes to STDs?

Our clinicians and researchers are working to advance prevention and treatment of STDs. Our AIDS Care Program offers primary and consultative medical care, counseling and testing, social services, and patient and family support groups for adults, adolescents and children with HIV.

Yale’s Center for Interdisciplinary Research on AIDS (CIRA) is New England's only National Institute of Mental Health-funded AIDS research center. CIRA brings together scientists from 25 disciplines to support research that combines behavioral, social and medical approaches to HIV prevention and treatment.

For chlamydia, we are involved in a National Institute of Health project to test a potential vaccine. For HPV, a Yale-led pilot study involves delivering the HPV vaccine to postpartum women, along with other efforts to improve immunization rates within the community.

“For society, focusing on prevention is the best approach, and we are seeing a lot of exciting advances in terms of vaccines for STDs,” Dr. Sheth says.