What STI testing and prophylaxis should be performed after a sexual assault?

STI Testing and Prophylaxis After Sexual Assault

Offer empiric antimicrobial prophylaxis immediately at the initial visit without waiting for test results, as follow-up compliance is often poor and early treatment prevents serious complications including pelvic inflammatory disease and infertility. 1

Immediate Prophylactic Treatment (Within 72 Hours)

The CDC recommends administering the following regimen at the first encounter: 1

• Ceftriaxone 125 mg IM (single dose) for gonorrhea coverage 1
• Azithromycin 1 g orally (single dose) OR Doxycycline 100 mg orally twice daily for 7 days for chlamydia coverage 1
• Metronidazole 2 g orally (single dose) for trichomoniasis and bacterial vaginosis coverage 1

Hepatitis B vaccination should be initiated immediately if the patient is not already vaccinated or immune, with the full 3-dose series at 0,1-2 months, and 4-6 months. 1

Initial Testing at Presentation

Baseline testing serves primarily as documentation rather than definitive exclusion of infection, since infectious agents may not have produced sufficient concentrations for detection immediately after exposure. 2, 3

Collect specimens from all sites of penetration or attempted penetration: 3

• Gonorrhea and chlamydia NAATs from genital, rectal, and pharyngeal sites based on exposure history 3
• Syphilis serology (both nontreponemal RPR/VDRL and treponemal tests) 3
• HIV testing (baseline laboratory-based Ag/Ab combination test) 3
• Hepatitis B serology if not previously vaccinated 3
• Vaginal wet mount and culture for Trichomonas vaginalis 2
• HSV viral culture or PCR if any vesicular or ulcerative lesions are present 3
• Pregnancy test at baseline 1

Preserve a serum sample from the initial visit for subsequent analysis if follow-up serologic tests become positive, which helps determine whether infection predated the assault. 2

Mandatory Follow-Up Testing Schedule

2-Week Follow-Up

Repeat bacterial STI testing (gonorrhea, chlamydia, trichomonas) at 2 weeks if prophylactic treatment was not given, as infectious agents may not produce sufficient concentrations for detection immediately after exposure. 2, 1

6-Week Follow-Up

Repeat HIV and syphilis serology at 6 weeks after the assault. 1

3-Month Follow-Up

Repeat HIV and syphilis serology at 3 months is critical because HIV antibody seroconversion may not be detectable until 3 months post-exposure, and syphilis serologic tests require 6-12 weeks to become positive after infection. 1

6-Month Follow-Up

Final HIV and syphilis serology at 6 months after the assault to definitively exclude infection acquired during the assault. 2, 1

Repeat pregnancy test at 2 weeks if the patient's period is late. 1

HIV Post-Exposure Prophylaxis (nPEP) Considerations

Consider nPEP within 72 hours if the assailant is known to be HIV-positive or there is substantial exposure risk (vaginal, rectal, or eye exposure). 2

For nPEP decision-making: 2

• Review local HIV epidemiology and assess risk for HIV infection in the assailant
• Evaluate circumstances of assault that might affect transmission risk
• If nPEP is started, perform CBC and serum chemistry at baseline 2
• Provide adequate medication to last until follow-up at 3-7 days, then reassess tolerance 2

For children, consult a specialist in treating pediatric HIV infection to select age-appropriate dosing if nPEP is considered. 2

Critical Counseling Points

Educate patients on the window period for infections and advise abstaining from sexual activity until 7 days after completing prophylactic treatment or until repeat testing confirms no infection. 1

Strongly encourage referral to Sexual Assault Referral Centre or equivalent counseling services as part of standard care. 1

Explain that condoms should be used for any sexual intercourse until STI prophylactic treatment is completed. 2

Common Pitfalls to Avoid

Failing to offer prophylactic treatment is a missed opportunity, as the prevalence of preexisting STDs is high in assault victims (43% in one study) and they have substantial additional risk of acquiring new infections (4% gonorrhea, 2% chlamydia, 12% trichomoniasis, 19% bacterial vaginosis). 4

Do not rely on a single negative test performed shortly after exposure—the window period for most STIs means early testing serves primarily as baseline documentation, not definitive exclusion of infection. 3

Testing too early and stopping there is the most critical error—a negative test at initial presentation does not rule out infection, and the structured follow-up schedule at 2 weeks, 6 weeks, 3 months, and 6 months is mandatory. 1, 3

Baseline and follow-up pregnancy testing is still indicated given the assault circumstances, even if prophylactic treatment was provided. 1