What should I tell a patient after a possible STI exposure (single unprotected sexual encounter with a partner known or suspected HIV‑positive) regarding evaluation, testing, post‑exposure prophylaxis, hepatitis B vaccination, and counseling?

Post-STI Exposure Counseling and Management

After a single unprotected sexual encounter with a partner known or suspected to be HIV-positive, you should immediately offer post-exposure prophylaxis (nPEP) within 72 hours, initiate hepatitis B vaccination if unvaccinated, provide empiric antimicrobial prophylaxis for bacterial STIs, and schedule mandatory follow-up testing at 2 weeks and 12 weeks. 1

Immediate Actions (Within 72 Hours)

HIV Post-Exposure Prophylaxis (nPEP)

• Initiate antiretroviral therapy immediately if the patient presents within 72 hours of exposure, as efficacy decreases significantly with delayed initiation 1
• The basic regimen consists of tenofovir disoproxil fumarate (TDF) plus emtricitabine (FTC) combined with a third agent, continued for 28 days 1
• Do not wait for source testing results to start nPEP—begin immediately and adjust if source testing later reveals negative HIV status 1
• If the source partner has sustained viral suppression (undetectable viral load), nPEP may not be necessary, but this requires documented evidence of suppression 1

Bacterial STI Prophylaxis

• Administer empiric treatment immediately without waiting for test results, as this prevents complications and provides reassurance 1, 2
• Ceftriaxone 250 mg IM single dose (covers gonorrhea) 1
• Azithromycin 1 g orally single dose (covers chlamydia) 1
• Metronidazole 2 g orally single dose (covers trichomoniasis and bacterial vaginosis) 1
• This combination may cause gastrointestinal side effects; counsel the patient accordingly 1

Hepatitis B Vaccination

• Initiate the hepatitis B vaccine series immediately if the patient has never been vaccinated or has unknown vaccination status 1
• Administer the first dose at the initial visit, with follow-up doses at 1-2 months and 4-6 months 1
• Post-vaccination testing for anti-HBs should occur 1-2 months after the final dose 1

Baseline Testing

Immediate Laboratory Evaluation

• Nucleic acid amplification tests (NAATs) for gonorrhea and chlamydia from all exposed anatomical sites (urethra/vagina, rectum if receptive anal intercourse, pharynx if receptive oral intercourse) 3, 4
• Syphilis serology using both nontreponemal (RPR or VDRL) and treponemal tests 3, 4
• HIV testing using laboratory-based antigen/antibody combination test 3, 4
• Hepatitis B serology (HBsAg and anti-HBs) if vaccination status is uncertain 3, 4
• Preserve a baseline serum sample for comparison with follow-up testing 1

Important Testing Considerations

• Baseline testing serves primarily as a reference point, as infections acquired from this exposure may not yet be detectable 1, 3
• Testing too early produces false-negative results—bacterial STIs need 1-2 weeks to reach detectable concentrations 1, 3

Mandatory Follow-Up Testing Schedule

2-Week Follow-Up

• Repeat NAATs for gonorrhea and chlamydia at all initially tested anatomical sites if baseline tests were negative and prophylaxis was given 1, 3, 2
• This detects infections that were in the incubation period at initial presentation 1, 3

6-Week Follow-Up

• Repeat HIV testing using laboratory-based antigen/antibody test, as the window period for HIV antibody development is 4-12 weeks 1, 3

12-Week (3-Month) Follow-Up

• Repeat HIV testing to definitively rule out HIV acquisition, as seroconversion may take up to 6 months in rare cases 1, 2
• Repeat syphilis serology (RPR/VDRL and treponemal tests), as antibody development requires 1-3 months 1, 2
• If any initial bacterial STI tests were positive and treated, mandatory retesting at 3 months due to high reinfection rates 3

6-Month Follow-Up

• Final HIV and syphilis testing if earlier tests were negative, to account for delayed seroconversion in rare cases 1, 2

Critical Counseling Points

Sexual Activity Restrictions

• Abstain from all sexual intercourse until completing the 7-day prophylactic treatment regimen 1, 2
• If follow-up testing reveals infection, abstain until treatment is completed and test-of-cure confirms clearance 1

Symptom Monitoring

• Seek immediate medical evaluation if any STI symptoms develop: urethral/vaginal discharge, dysuria, genital ulcers, rash, or anorectal symptoms 1
• Many STIs are asymptomatic (70% of HSV and trichomoniasis, 53-100% of extragenital gonorrhea/chlamydia), so absence of symptoms does not rule out infection 5

Partner Notification

• All sexual partners from the preceding 60 days must be evaluated and treated, even if asymptomatic 3
• The source partner (if known) should be encouraged to seek HIV care if not already engaged 1

Window Period Education

• Explain that negative baseline tests do not rule out infection—the exposure may be too recent for detection 1, 3
• Emphasize the critical importance of completing all follow-up testing appointments 1, 2

Common Pitfalls to Avoid

Timing Errors

• Do not delay nPEP initiation while awaiting source testing—the 72-hour window is critical for efficacy 1
• Do not rely solely on baseline testing—infections may not be detectable for 1-2 weeks (bacterial) or 3-6 months (HIV, syphilis) 1, 3

Testing Gaps

• Do not omit site-specific testing based on exposure history—test pharynx for gonorrhea if receptive oral sex occurred, rectum for gonorrhea/chlamydia if receptive anal sex occurred 3, 4
• Do not skip the 12-week follow-up even if 6-week HIV testing is negative—rare delayed seroconversion can occur 1, 2

Treatment Errors

• Do not withhold empiric bacterial STI prophylaxis while awaiting test results—treatment prevents complications and is recommended regardless of baseline test results 1, 2
• Do not assume condom use eliminates risk—condoms provide incomplete protection, especially for ulcerative STIs like syphilis and HSV 3

Special Considerations for High-Risk Source Partners

Known HIV-Positive Source

• If the source has documented sustained viral suppression (undetectable viral load on multiple tests), transmission risk is negligible, but nPEP may still be offered based on patient preference 1
• If the source has known viremia or unknown viral load, nPEP is strongly recommended 1
• Obtain information about the source's antiretroviral treatment history and resistance testing if available, as this may guide nPEP regimen selection 1

Unknown Source Status

• If the source's HIV status is unknown but they belong to a high-prevalence population (men who have sex with men, people who inject drugs, sex workers), offer nPEP on a case-by-case basis 1
• Consider local HIV prevalence rates when making this determination 1

Ongoing Risk Assessment

Future Screening Recommendations

• If the patient has ongoing high-risk behaviors (multiple partners, substance use during sex, transactional sex), recommend screening every 3-6 months indefinitely 3, 4
• Provide counseling on consistent condom use and consider HIV pre-exposure prophylaxis (PrEP) if high-risk behaviors continue 3