Post-exposure prophylaxis in emergency situations
What PEP is
- Short course of antimicrobial or immunological therapy after a defined exposure to prevent established infection
- Time-critical - hours matter, not days
The exposures to assess at every presentation
| HIV | Antiretroviral PEP, within 72 h, 28 days |
| Hepatitis B | HBIG +/- vaccine, ideally <24 h, within 72 h (sexual) / 7 days (percutaneous) |
| Hepatitis C | No PEP exists - surveillance and early treatment if seroconversion |
| Bacterial STI | Empirical treatment or doxycycline PEP in selected populations |
| Tetanus | Vaccine +/- immunoglobulin by wound type and vaccination history |
| Pregnancy | Emergency contraception |
| Rabies/ABLV | Vaccine + immunoglobulin after bat or overseas animal exposure |
| Meningococcal, pertussis, measles, varicella | Contact prophylaxis - notify public health |
- *Never treat this as a single-disease consultation* - the sexual assault or needlestick presentation requires all of the above plus psychosocial care
Per-exposure HIV transmission risk
- Per-exposure HIV transmission risk (source known positive, untreated)
| Exposure | Risk |
|---|---|
| Receptive anal intercourse | ~1 in 70-150 (highest sexual route) |
| Insertive anal | ~1 in 900 |
| Receptive vaginal | ~1 in 1000 |
| Insertive vaginal | ~1 in 1200 |
| Needlestick (percutaneous, hollow-bore) | ~1 in 300 (0.3%) |
| Mucous membrane splash | ~1 in 1000 |
| Sharing injecting equipment | ~1 in 150 |
- Hepatitis B needlestick from an HBeAg-positive source: ~30% (far more transmissible than HIV or HCV)
- Hepatitis C needlestick: ~1.8%
- *U=U: an HIV-positive source with a sustained undetectable viral load does not transmit sexually - PEP is not indicated*
- Australia: most non-occupational PEP is prescribed to men who have sex with men; occupational transmission of HIV in Australian healthcare is now vanishingly rare
The window for prophylaxis
- Window between exposure and systemic infection:
- Local replication in dendritic cells and mucosal CD4 cells over 24-72 h
- Migration to regional lymph nodes, then systemic dissemination by ~5 days
- Antiretrovirals given before dissemination abort the infection - hence the 72 h ceiling and the steep benefit of earlier initiation
- Efficacy evidence: animal models, the retrospective occupational case-control study (~81% risk reduction with zidovudine), and perinatal transmission trials
- No RCT exists and none will be done
- Hepatitis B: HBIG provides immediate passive antibody; vaccine provides active immunity - together they give ~90% protection when given early
Risk assessment - the three questions
1. What was the exposure? Route, fluid type, volume, duration, integrity of skin/mucosa, needle bore and whether hollow
2. What is the source's status? HIV, HBV, HCV serology; if HIV positive - on treatment? viral load? resistance history?
- Attempt source testing with consent; a rapid HIV test on the source may avert unnecessary PEP
3. What is the exposed person's status? HIV, HBV immunity and vaccination history, HCV, pregnancy, renal function, current medications
Baseline testing of the exposed person
Baseline testing of the exposed person - before the first dose, but do not wait for results
- HIV antigen/antibody, HBsAg, anti-HBs, anti-HBc, anti-HCV (and HCV RNA if high risk)
- Syphilis serology, gonorrhoea/chlamydia NAAT from all exposed sites (throat, rectum, urethra/vagina)
- UEC, LFT, FBE (baseline for tenofovir)
- Pregnancy test
- Documenting a negative baseline HIV test protects the patient and the clinician medicolegally
Decision rules - HIV PEP
Decision rules - HIV PEP
- Indicated if: significant exposure AND source HIV-positive with detectable/unknown viral load, OR source of unknown status from a high-prevalence group, AND presentation within 72 h
- Not indicated if: source has sustained undetectable viral load (U=U), exposure to intact skin, exposure to non-infectious fluid (urine, faeces, vomit, saliva without blood), >72 h elapsed, or the exposed person is already HIV-positive
- Use the ASHM PEP decision tool where available
HIV PEP
A. HIV PEP
- Start as soon as possible - ideally within hours; efficacy is greatest within 24 h; the outer limit is 72 h
- Duration: 28 days
- Give the first dose in the emergency department - do not defer to an outpatient appointment
- Regimens (risk-stratified; all 28 days):
- Two-drug: tenofovir disoproxil 300 mg + emtricitabine 200 mg (or lamivudine) daily - suitable for most exposures; affordable generics now allow GP prescribing on private script
- Three-drug: add an integrase inhibitor - dolutegravir 50 mg daily (or raltegravir 400 mg bd) - for the highest-risk exposures, known resistance, or source with detectable viraemia
- Adherence is the main determinant of efficacy - anticipate nausea, diarrhoea, headache; prescribe antiemetics; provide a full 28-day supply where possible
- Dolutegravir: counsel about weight gain and insomnia; check for interactions (polyvalent cations, metformin, rifampicin)
- Tenofovir disoproxil: monitor renal function; avoid or adjust in significant CKD
- Refer to a sexual health or infectious diseases service for all cases
Hepatitis B PEP
B. Hepatitis B PEP
- Depends on the exposed person's immune status and the source
| Exposed person | Action |
|---|---|
| Documented anti-HBs >=10 mIU/mL (responder) | No action |
| Unvaccinated / unknown | HBIG 400 IU IM (ideally <24 h) + start the vaccine course (0, 1, 6 months) |
| Known non-responder | HBIG x2 doses, 1 month apart; revaccinate |
| Vaccinated, anti-HBs unknown | Test urgently; give vaccine booster, add HBIG if source HBsAg-positive and result unavailable |
- Window: ideally <24 h; up to 72 h for sexual exposure, up to 7 days for percutaneous
Hepatitis C
C. Hepatitis C
- No prophylaxis and no immunoglobulin
- Surveillance: HCV RNA at 4-6 weeks, anti-HCV at 3 and 6 months
- Treat acute infection if seroconversion occurs - DAAs are highly effective and PBS-funded
Bacterial STIs and other exposures
D. Bacterial STIs and other exposures
- Sexual assault: empirical treatment for chlamydia and gonorrhoea (azithromycin/doxycycline + ceftriaxone), emergency contraception, forensic examination if consented, dedicated sexual assault service, trauma-informed care
- Doxycycline PEP (doxy-PEP): doxycycline 200 mg within 72 h of condomless sex reduces syphilis and chlamydia, and to a lesser degree gonorrhoea
- Recommended in Australia for selected gay, bisexual and other men who have sex with men and trans women with recurrent bacterial STIs; not recommended for cisgender women (no demonstrated benefit); counsel on tetracycline resistance
- Tetanus: vaccine +/- tetanus immunoglobulin per wound classification and vaccination history
- Rabies/Australian bat lyssavirus: wound care, rabies vaccine + immunoglobulin - discuss with the state communicable disease unit urgently
Follow-up - structured and non-negotiable
E. Follow-up - structured and non-negotiable
| Time | Tests |
|---|---|
| Day 3-7 | Review tolerability, adherence, results of source testing (stop PEP if source proves negative or undetectable), UEC/LFT |
| Week 4-6 | HIV Ag/Ab, HCV RNA, syphilis serology, STI NAAT, UEC/LFT |
| Month 3 | HIV Ag/Ab (the definitive test in the fourth-generation era), HCV, syphilis |
| Month 6 | Only if HCV co-exposure or immunocompromised |
Alongside the prescription
F. Alongside the prescription
- Counsel on avoiding onward transmission until testing complete (condoms, no blood/organ/tissue donation, no sharing injecting equipment, safe breastfeeding advice)
- Psychological support - distress is high and adherence tracks it
- Discuss PrEP - a person presenting for PEP is by definition a candidate for PrEP; transition directly at day 28 where ongoing risk persists
- Occupational exposure: incident report, staff health, review of sharps practice; *never re-sheathe a needle*
- Notify public health where required
Exposure settings
- Occupational needlestick and sharps injuries; splash exposures
- Condomless sex, sexual assault, injecting drug use, tattooing/piercing with unsterile equipment
- PrEP - the longer-term counterpart; PEP presentations are the main PrEP recruitment opportunity
- U=U (undetectable = untransmittable) - reframes source risk assessment
- Hepatitis B vaccination status and healthcare worker immunity requirements
- Emergency contraception, sexual assault services, forensic medicine
- Doxycycline PEP and rising tetracycline resistance in Neisseria gonorrhoeae and Mycoplasma genitalium
- Stigma, disclosure and mental health; adherence
- Rabies / Australian bat lyssavirus, tetanus, meningococcal contact prophylaxis
Effectiveness and completion
- PEP is highly effective when started early and taken completely - failures are almost always late initiation, non-adherence, or ongoing exposure during the course
- Completion rates are only ~60-70% - adverse effects and loss to follow-up; the follow-up appointment is part of the treatment
- Seroconversion despite PEP is rare; when it occurs, resistance testing is mandatory before selecting long-term ART
- Fourth-generation HIV testing means the 3-month test is definitive; 6-month testing is reserved for HCV co-exposure or immunosuppression
- Hepatitis B: HBIG + vaccine given promptly prevents ~90% of transmissions; check anti-HBs 1-2 months after the final vaccine dose
- Hepatitis C: ~25% of acute infections clear spontaneously; the rest are curable with DAAs - the reason surveillance matters despite the absence of prophylaxis
- Psychological sequelae - anxiety, insomnia, relationship disruption - often outlast the medical risk
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