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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Chlamydia/gonorrhea: screen all sexually active women age <=24 and women >=25 at increased risk; evidence insufficient for routine screening in low-risk heterosexual men
- HIV: USPSTF screens ages 15-65 at least once and all pregnant persons; CDC recommends ages 13-64 at least once with opt-out approach
- Syphilis: screen pregnant persons universally early in pregnancy and screen nonpregnant adults/adolescents at increased risk
- MSM: screen at least annually for HIV, syphilis, chlamydia, and gonorrhea at sites of exposure; every 3-6 months if high risk
- Use NAAT for chlamydia/gonorrhea and collect anatomic-site-specific tests based on exposure: urine/urethral, vaginal/cervical, rectal, pharyngeal
Overview
STI screening is a high-yield preventive medicine topic because many infections are asymptomatic but cause infertility, ectopic pregnancy, chronic pelvic pain, congenital infection, neonatal disease, HIV acquisition risk, and transmission. Screening recommendations depend on age, sex assigned at birth, pregnancy status, sexual practices, number of partners, condom use, prior STIs, HIV/PrEP status, local epidemiology, and sites of exposure. Step 2 CK often tests who should be screened, which specimen to collect, and how pregnancy changes urgency.
Epidemiology
Chlamydia is the most commonly reported bacterial STI in the United States, with highest rates in adolescents and young adults. Gonorrhea and syphilis remain major public health concerns, including rising congenital syphilis in the US. STIs disproportionately affect adolescents and young adults, MSM, transgender persons, persons with HIV, persons with unstable housing, incarcerated persons, people who exchange sex, and communities with reduced access to confidential preventive care.
Screening Indications and Risk Features
Symptoms
Asymptomatic sexually active woman age <=24: screen for chlamydia and gonorrhea annually
Woman age >=25 with new partner, multiple partners, partner with STI, inconsistent condom use, sex work, or high-prevalence setting: screen for chlamydia/gonorrhea
Pregnancy: screen early for HIV, syphilis, hepatitis B, hepatitis C, and risk-based chlamydia/gonorrhea; repeat high-risk tests later in pregnancy
MSM: screen HIV, syphilis, chlamydia, and gonorrhea at sites of exposure at least annually
Urethral discharge, cervicitis, PID symptoms, genital ulcer, rash involving palms/soles, or testicular pain requires diagnostic evaluation and often empiric treatment
Sexual assault requires time-sensitive STI prophylaxis, emergency contraception, HIV PEP assessment, and forensic/advocacy support
Signs
Mucopurulent cervicitis, cervical friability, urethral discharge, epididymal tenderness, or pelvic tenderness suggests active infection
Painless chancre, diffuse rash including palms/soles, condyloma lata, or neurologic/ocular symptoms suggest syphilis stage-specific disease
Extragenital infections are often asymptomatic; pharyngeal and rectal sites require site-specific testing based on exposure
Normal exam does not exclude chlamydia, gonorrhea, HIV, syphilis, or hepatitis infection
Screening Tests
First-line
Chlamydia/gonorrhea NAATPreferred test. Use vaginal swab, cervical swab, first-catch urine, rectal swab, or pharyngeal swab depending on anatomy and exposure
HIV antigen/antibody testScreen at least once in adolescents/adults and all pregnant persons; repeat at least annually for ongoing risk. Use HIV RNA if acute infection suspected
Syphilis serologyTraditional algorithm: nontreponemal RPR/VDRL followed by treponemal confirmation; reverse sequence algorithms are also common
Second-line
Hepatitis B screeningUniversal adult HBV screening is now recommended by CDC at least once using triple panel: HBsAg, anti-HBs, total anti-HBc; pregnancy screening with HBsAg remains critical
Hepatitis C screeningUSPSTF: screen adults age 18-79 and all pregnant persons during each pregnancy in many current US practices; repeat if ongoing risk
Trichomonas testingConsider in symptomatic women and in women with HIV; routine population screening varies by risk and setting
Specialist
PrEP evaluationFor patients at substantial HIV risk: HIV test, renal function, hepatitis B status, STI screening, pregnancy test when relevant, and adherence counseling
Public health reporting and partner servicesMany STIs are reportable. Partner notification, expedited partner therapy where legal, and test-of-cure/retesting rules reduce reinfection
Screening Recommendations
CDC STI Treatment Guidelines; USPSTF STI Screening Recommendations1
Chlamydia and gonorrhea
- Screen sexually active women age <=24 annually
- Screen women age >=25 if increased risk
- Pregnancy: screen women <=24 and older women at increased risk; retest in third trimester if ongoing risk
- MSM: screen at least annually at all sites of exposure; every 3-6 months if high risk or on PrEP
- Retest approximately 3 months after treatment to detect reinfection
2
HIV and syphilis
- HIV: screen ages 15-65 under USPSTF; younger/older if increased risk; all pregnant persons including labor if status unknown
- CDC opt-out HIV screening: ages 13-64 at least once in healthcare settings; at least annually if ongoing risk
- Syphilis: screen all pregnant persons early; repeat later in pregnancy if high risk or high-prevalence setting per local guidance
- Screen nonpregnant persons at increased syphilis risk, including MSM, persons with HIV, and high-prevalence communities
3
Hepatitis and vaccination linkage
- Hepatitis B: screen adults at least once and pregnant persons; vaccinate susceptible adults according to ACIP
- Hepatitis C: screen adults age 18-79 and pregnant persons; repeat if injection drug use or ongoing risk
- Offer HPV vaccination through age 26 and shared decision-making age 27-45
- Offer hepatitis A/B vaccination when risk factors or susceptibility are present
4
Confidential, patient-centered care
- Take a nonjudgmental sexual history using partners, practices, protection, past STIs, pregnancy intention, and prevention of HIV/STIs
- Use patient-preferred names, pronouns, and anatomy-specific screening for transgender and gender-diverse patients
- Counsel on condoms, PrEP, doxy-PEP eligibility when applicable, vaccination, and partner treatment
- Do not use Pap smear as an STI screening test; cervical cancer screening and STI NAATs are different
Complications
- Chlamydia/gonorrhea: PID, infertility, ectopic pregnancy, chronic pelvic pain, epididymitis, disseminated gonococcal infection
- Syphilis: Neurosyphilis, ocular syphilis, cardiovascular syphilis, congenital syphilis, stillbirth, neonatal death
- HIV: Delayed diagnosis, opportunistic infection, transmission, and missed PrEP opportunities
- Pregnancy/neonatal harms: Congenital syphilis, neonatal conjunctivitis, pneumonia, HIV transmission, HBV transmission
- Reinfection: Common if partners are untreated; retesting and partner services are essential
USMLE Step 2 CK Exam Tips
- 1Chlamydia/gonorrhea screen: sexually active women <=24 and older women at increased risk
- 2NAAT is the preferred test for chlamydia and gonorrhea
- 3MSM require site-specific screening based on exposure — urine alone misses rectal/pharyngeal infections
- 4HIV screening: USPSTF 15-65; CDC routine opt-out 13-64. Exams may accept either depending on wording
- 5Pregnancy: screen for HIV and syphilis early; unknown HIV status in labor = rapid testing
- 6Positive chlamydia/gonorrhea treatment should be followed by retesting at ~3 months for reinfection
- 7Pap smear does not screen for chlamydia/gonorrhea
- 8Genital ulcer differential: syphilis is painless; HSV is painful vesicles/ulcers
practicetest your knowledge on sti screening recommendationsApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — preventive medicine and beyond.
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