Sexual Health Update: Advances in the Prevention & Treatment of Sexually Transmitted Infections

By Rick Isenberg - 12/18/2023


The surge in sexually transmitted infections (STIs) continues in the US with 2.5 million cases reported to the Centers for Disease Control (CDC) in 2021. Cases of syphilis in women jumped 49% compared to the prior year; congenital syphilis (when syphilis passes from mother to baby during pregnancy) was up 24% when compared to 2020. Rates of gonorrhea have increased 118% since their historic low in 2009. The CDC as estimated that one in five Americans (20%) have a STI in any given year. Young adults ages 20-34 have the highest rates of infection. The World Health Organization reports that the rates of non-classical STIs (such as Shigella, Hepatitis A, Zika, and lymphogranuloma venereum (LGV)) are also on the rise.

Because STIs often do not show symptoms despite their long-term health consequences, prevention and screening are essential to contain the spread of the diseases. With directed, government-supported efforts around the world, important advances in prevention and treatment are becoming available. I summarize a few of the most exciting recent advances in the world of STIs in the sections below.


In what amounts to a major advance in prevention of STIs, the CDC released proposed guidelines in October 2023 for the use of the antibiotic DOXYCYCLINE as post-exposure prophylaxis to prevent infection following possible exposure to gonorrhea, chlamydia, and syphilis. This approach, known as doxyPEP, may help to counter the recent surge in these infections in the US and prompt uptake by other countries around the world.

The proposed guidelines recommend that a single 200 mg dose of oral doxycycline taken within 72 hours after oral, anal, or vaginal sex should be considered for gay, bisexual, and other men who have sex with men (MSM) and for transgender women who have had gonorrhea, chlamydia, or syphilis at least once in the past year. This is a strong recommendation supported by data from clinical trials.

The guidelines also say that doxyPEP “could be considered” for MSM and transgender women who have not had a recent STI if they “will be participating in sexual activities that are known to increase the likelihood of exposure to STIs, e.g., during weekend events, cruises and festivals.”

However, citing the lack of evidence, the guidelines do not recommend the use of doxyPEP for cisgender women, cisgender heterosexual men, transgender men, or other queer or nonbinary people. The CDC does leave the door open to clinicians to offer doxyPEP to these populations on a case-by-case basis following risk assessment.

DoxyPEP should be used in the context of a comprehensive sexual health approach that includes risk reduction counseling, STI screening and treatment, vaccination, and access to HIV pre-exposure prophylaxis (PrEP), HIV care and other services.

HIV Prevention

An estimated 38 million people are living with HIV worldwide, with up to 1.5 million new cases of HIV reported each year. Due to advances in prevention, the rate of HIV infection worldwide has dropped by 54% since the peak of the epidemic in 1996.

Pre-exposure prophylaxis (PrEP) for HIV prevention first became available in the US in 2012 and radically changed the risk of getting HIV for sexually active adults and adolescents. Daily oral dosing of a potent anti-viral combination has been shown to reduce the risk of HIV transmission by 99%. Maximum protection for receptive anal sex (bottoming) occurs after about 7 days of use. For receptive vaginal sex and injection drug use, PrEP pills reach maximum protection in about 21 days. PrEP is recommended for gay, bisexual, and other MSM, transgender women, and men and women who inject drugs.

“On-demand” oral PrEP, also known as the 2:1:1 method, has been shown to be safe and effective, reducing HIV transmission by 86% for men who have anal sex without a condom. The 2:1:1 method involves taking 2 pills 2-24 hours before possible sexual exposure (closer to 24 hours is preferred), followed by one pill daily for the next two days. The 2:1:1 method is recommended for MSM but not for heterosexual men and women, IV drug users, or transgender persons.

You can find a clinician who prescribes PrEP through the national PrEP Clinician Locator ( Free PrEP and STI testing for men who have sex with men can be obtained through MISTR (

Post-Exposure Prophylaxis (PEP) for HIV is also available in the US and is effective prevention for people who have risky sex infrequently. PEP is the use of antiretroviral drugs for 28 days after a single high-risk sexual episode to prevent the person from getting HIV. For persons with ongoing risky sexual activity, the CDC recommends beginning PrEP immediately upon completion of the 28-day PEP treatment.

STI Vaccines

Safe and effective vaccines are available for two STIs: Hepatitis B (a serious disease that may cause lifelong infection, cirrhosis, liver failure, and liver cancer) and HPV (which is known to cause cervical and anal cancer). One of the major routes of transmission for Hepatitis B among heterosexual, bisexual, and homosexual men and women is through sexual contact. Hepatitis B vaccine is recommended by CDC for infants, children, adolescents, and adults. Unfortunately, up to 70% of adults in the US report that they are unvaccinated.

The HPV vaccine is recommended by CDC for routine vaccination of children, adolescents, and young adults through age 26, as well as for adults at high risk of infection. The HPV vaccine has been incorporated into routine vaccination programs in 111 countries around the world. The incidence of infection with cancer-causing HPV in young adult women have dropped 81% since the vaccine was introduced in 2006.

Research into vaccines against genital herpes is advanced and ongoing. Chlamydia vaccines are in early clinical trials. This fall, FDA granted Glaxo-Smith-Kline fast track designation for its investigational vaccine against gonorrhea, now in Phase 2 trials; fast track designation allows for accelerated development and expedited review of this vaccine.

Work on new HIV vaccines continue, leveraging the remarkable success of mRNA vaccines for COVID as well as other novel approaches. Multiple promising investigative vaccines have failed to be effective in clinical trials. The HIV virus’s ability to mutate and diversify itself remains the greatest challenge to developing an effective vaccine. And the research continues.


It serves all of us to stay current with the global developments in STI prevention and treatment as people of all ages and sexual orientations are increasingly at risk for these potentially serious infections. In all likelihood, you know someone whose sexual behavior puts them at risk. Please share this article widely.


  • Bisexual: A person who is attracted to both people of their own gender and other genders.
  • CDC: the US Centers for Disease Control and Prevention
  • Cisgender person: Individuals whose current gender identity is the same as the sex they were assigned at birth.
  • FDA: the US Food and Drug Administration
  • Gay: A person who is attracted primarily to members of the same gender. Gay is most frequently used to describe men who are attracted primarily to other men, although it can be used for men and women.
  • Gender: The cultural roles, behaviors, activities, and attributes expected of people based on their sex.
  • Heterosexual or Straight: A man who is primarily attracted to women or a woman who is primarily attracted to men.
  • HIV: human immunodeficiency virus.
  • HPV: human papilloma virus. The virus known to cause cervical and anal cancer as well as other less serious infections.
  • Lesbian: A woman who is primarily attracted to other women.
  • MSM: men who have sex with other men.
  • PEP: post-exposure prophylaxis. Refers to the use of antiviral medication to prevent the acquisition of HIV following known or possible sexual exposure to an individual with HIV.
  • PrEP: pre-exposure prophylaxis. Refers to the preventative use of antiviral medication to prevent the acquisition of HIV through risky sexual activities.
  • STI: sexually transmitted infection. Also referred to as STD (sexually transmitted disease)
  • Transgender person: A person whose gender identity or expression is different from their sex assigned at birth.
  • Transgender man: A person assigned female at birth who identifies as male.
  • Transgender woman: A person assigned male at birth who identifies as female.


Advances in the treatment and prevention of HIV. Hospital Medicine July 2023.

Centers for Disease Control and Prevention. Guidelines for the Use of Doxycycline Post-Exposure Prophylaxis for Bacterial Sexually Transmitted Infection (STI) Prevention; Request for Comment and Informational Presentation. 2 October 2023.

Centers for Disease Control and Prevention. Hepatitis B Fact Sheet.

Centers for Disease Control and Prevention. Preexposure Prophylaxis for the Prevention of HIV Infection in the United States—2021 Update.

Centers for Disease Control and Prevention. Sexually Transmitted Infections Treatment Guidelines, 2021.

Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance 2021.

Global roadmap for advancing development of vaccines against sexually transmitted infections: updates and next steps. Vaccine, 34:26.

World Health Organization. STIs in 2022: emerging and re-emerging outbreaks. WHO STI update.
World Health Organization. Sexually Transmitted Infections Fact Sheet, 2023.

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