Residency · Residency · Preventive Medicine
Sexually Transmitted Infection Prevention and Control
Overview
STIs are a major public health burden: ~26 million new infections annually in the U.S. Direct medical costs estimated at $16 billion/year in the U.S. Rising rates of syphilis (including congenital syphilis), gonorrhea, and chlamydia despite available interventions. STI prevention requires a combination of behavioral, biomedical, and structural interventions. Disproportionate burden among young people, MSM, racial/ethnic minorities, and those with limited healthcare access.
Epidemiology of Major STIs
Chlamydia (Chlamydia trachomatis)
Most commonly reported bacterial STI in the U.S. (~1.6 million reported cases/year) Often asymptomatic (up to 70% of women, 50% of men) Complications: PID, ectopic pregnancy, infertility, reactive arthritis. Screening: sexually active women <25 years (annually), older women with risk factors (USPSTF A recommendation) Treatment: doxycycline 100 mg BID x 7 days (preferred) or azithromycin 1g single dose.
Gonorrhea (Neisseria gonorrhoeae)
~680,000 reported cases/year in the U.S. Increasing antimicrobial resistance is an urgent public health threat. Can infect cervix, urethra, rectum, pharynx, and eyes. Complications: PID, epididymitis, disseminated gonococcal infection. Treatment: ceftriaxone 500 mg IM single dose (dual therapy with azithromycin no longer recommended unless chlamydia co-infection suspected) Test of cure recommended for pharyngeal infections.
Syphilis (Treponema pallidum)
Resurgence in the U.S.: rates at highest levels since the 1950s. Congenital syphilis rates have increased >10-fold since 2012 (~3,700 cases in 2022) Stages: primary (chancre), secondary (rash, condylomata lata), latent (early <1 year, late >1 year), tertiary (gummas, cardiovascular, neurosyphilis) Screening: all pregnant women at first prenatal visit (many states mandate); MSM, HIV-positive individuals, high-risk populations. Treatment: benzathine penicillin G 2.4 million units IM (primary/secondary/early latent); weekly x 3 for late latent/unknown duration. Jarisch-Herxheimer reaction: fever, myalgias within 24 hours of treatment (self-limited)
HIV
~1.2 million people living with HIV in the U.S.; ~13% unaware of their status. ~30,000 new infections/year (declining but unevenly) Disproportionate burden: Black and Hispanic MSM, transgender women, Southern U.S. USPSTF: screen all adolescents and adults aged 15-65 (A recommendation) Treatment as Prevention (TasP): undetectable viral load = untransmittable (U=U)
Herpes Simplex Virus (HSV)
HSV-2 seroprevalence: ~12% of U.S. adults. Recurrent genital ulcers; asymptomatic shedding common. Neonatal herpes: life-threatening; risk highest with primary maternal infection near delivery. No cure; suppressive therapy (valacyclovir) reduces outbreaks and transmission. CDC does not recommend routine serologic screening in asymptomatic individuals.
Human Papillomavirus (HPV)
Most common STI; ~43 million infections/year in the U.S. High-risk types (16, 18): cervical, anal, oropharyngeal, vulvar, vaginal, penile cancer. Low-risk types (6, 11): genital warts. HPV vaccine (9-valent): recommended ages 9-26; shared clinical decision-making 27-45. Vaccination prevents ~90% of HPV-related cancers when administered before exposure. Cervical cancer screening: HPV testing and/or Pap smear per USPSTF guidelines.
| STI | Annual U.S. Cases | Screening Recommendation | First-Line Treatment | Key Complication |
|---|---|---|---|---|
| Chlamydia | ~1.6 million reported | Women <25 annually (USPSTF A) | Doxycycline 100mg BID × 7 days | PID, infertility, ectopic pregnancy |
| Gonorrhea | ~680,000 reported | Women <25 and at-risk populations | Ceftriaxone 500mg IM × 1 | PID, disseminated infection; AMR threat |
| Syphilis (P&S) | Rising rapidly | Pregnant women, MSM, HIV+ | Benzathine penicillin G 2.4M units IM | Congenital syphilis, neurosyphilis |
| HIV | ~30,000 new/year | All adults 15-65 (USPSTF A) | ART (lifelong); TasP (U=U) | Immunodeficiency, opportunistic infections |
| HPV | ~43 million/year | Cervical screening per USPSTF | No treatment for infection; vaccine prevention | Cervical, anal, oropharyngeal cancer |
| HSV-2 | ~12% seroprevalence | Not recommended for asymptomatic | Valacyclovir (suppressive or episodic) | Neonatal herpes, recurrent ulcers |
Prevention Strategies
Behavioral Interventions
Comprehensive sex education: associated with delayed sexual debut, increased condom use, reduced STI rates. Condom promotion: male latex condoms reduce STI transmission by 60-80% with consistent use. Risk reduction counseling: brief, patient-centered counseling in clinical settings. Partner notification and treatment: essential for breaking transmission chains.
Biomedical Interventions
PrEP (Pre-Exposure Prophylaxis) for HIV
Highly effective for HIV prevention: oral TDF/FTC (Truvada) reduces sexual acquisition by ~99% with daily adherence. Injectable cabotegravir (Apretude): every-2-month injection; superior to oral PrEP in clinical trials. USPSTF A recommendation: prescribe PrEP for individuals at high risk for HIV. Indications: MSM with inconsistent condom use, serodiscordant couples, PWID, individuals with recent STI. Monitoring: HIV testing before initiation and every 3 months, renal function, STI screening. Uptake disparities: significantly lower among Black and Hispanic individuals and women despite higher HIV risk.
PEP (Post-Exposure Prophylaxis)
28-day course of antiretroviral therapy initiated within 72 hours of potential HIV exposure. Three-drug regimen: TDF/FTC + raltegravir or dolutegravir. Used for occupational (needlestick) and non-occupational (sexual assault, condomless sex) exposures.
Doxy-PEP (Doxycycline Post-Exposure Prophylaxis)
Doxycycline 200 mg taken within 72 hours after condomless sex. Reduces incidence of chlamydia, syphilis, and possibly gonorrhea among MSM and transgender women. CDC interim guidance issued 2023 for MSM and transgender women. Concerns about promoting tetracycline resistance and impact on microbiome.
Structural Interventions
Expanding access to STI testing and treatment (free clinics, pharmacy-based testing, self-collection kits) Title X family planning clinics: critical source of STI services for low-income populations. Addressing poverty, racism, and housing instability as upstream drivers of STI disparities. Decriminalizing sex work: evidence suggests reducing criminalization improves STI testing and treatment uptake. Addressing STI stigma through inclusive, non-judgmental clinical environments.
Congenital Syphilis Prevention
Congenital syphilis is entirely preventable with adequate prenatal screening and treatment. Rising rates reflect failures in prenatal care access, screening, and treatment. Risk factors: late or no prenatal care, substance use, prior STI, homelessness. Prevention: universal prenatal syphilis screening at first visit; repeat screening in third trimester and at delivery in high-prevalence areas. Treatment of maternal syphilis with benzathine penicillin prevents >95% of congenital syphilis cases.
Partner Services and Contact Tracing
Partner notification (also called partner services): informing sexual contacts of STI exposure. Methods: patient referral (patient notifies partners), provider referral (health department notifies), contract referral (patient agrees to notify within timeframe, health department follows up) Expedited Partner Therapy (EPT): providing prescriptions or medications for partners without clinical examination. Legal in most states; recommended by CDC for chlamydia and gonorrhea. Not recommended for MSM (HIV/STI screening should be performed) or syphilis. Disease Intervention Specialists (DIS): public health workers who conduct partner services, particularly for syphilis and HIV.
<image>A graph showing the trends in reported STI cases in the United States from 2000 to 2024 for chlamydia, gonorrhea, and primary/secondary syphilis. The graph shows the dramatic increase in syphilis rates, steady increases in gonorrhea, and high sustained rates of chlamydia. A secondary y-axis or inset shows the alarming rise in congenital syphilis cases over the same period. CDC surveillance data style line graph for STI epidemiology education.</image>
<image>A diagram showing the biomedical prevention toolkit for STIs, organized as a spectrum from pre-exposure to post-exposure. Pre-exposure: HPV vaccination, PrEP (oral and injectable), condoms, circumcision. Post-exposure: PEP (within 72 hours), Doxy-PEP (within 72 hours for bacterial STIs). Ongoing: screening programs, treatment as prevention (U=U for HIV), expedited partner therapy. Each intervention includes its evidence-based efficacy estimate. STI prevention education infographic.</image>
Clinical Pearls
Congenital syphilis is a sentinel event for healthcare system failure -- every case represents a missed opportunity for prenatal screening and treatment. PrEP is drastically underutilized among those who would benefit most -- only ~36% of individuals with PrEP indications have been prescribed it, with significant racial disparities. The shift from azithromycin to doxycycline as first-line chlamydia treatment reflects growing macrolide resistance, particularly in Mycoplasma genitalium. Risk compensation (increased risky behavior offsetting biomedical prevention) has NOT been conclusively demonstrated with PrEP in clinical trials. For boards: know the USPSTF screening recommendations for chlamydia, syphilis, HIV, and Hep B/C; know PrEP indications and monitoring; understand expedited partner therapy.
References
- CDC. Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR. 2021;70(4):1-187.
- USPSTF. Screening for Chlamydia and Gonorrhea. JAMA. 2021;326(10):949-956.
- Molina JM, et al. Doxycycline as post-exposure prophylaxis for STIs among men who have sex with men. N Engl J Med. 2023;388(14):1296-1306.
- Grant RM, et al. Preexposure chemoprophylaxis for HIV prevention in men who have sex with men. N Engl J Med. 2010;363(27):2587-2599.
- Kimball A, et al. Missed opportunities for prevention of congenital syphilis -- United States, 2018. MMWR. 2020;69(22):661-665.
