2.4 HIV Prevention (PrEP & PEP), Viral Hepatitis, Mycoplasma genitalium & Ectoparasites
Key Takeaways
For people exposed through receptive vaginal sex, HIV PrEP options are daily oral TDF/FTC, injectable cabotegravir every 2 months, and twice-yearly subcutaneous lenacapavir (FDA-approved June 2025); oral TAF/FTC is not approved for this exposure.
CDC's 2024 doxycycline post-exposure prophylaxis (doxy-PEP) recommendation covers men who have sex with men and transgender women, not cisgender women.
CDC recommends hepatitis B screening of all adults at least once with a triple panel (HBsAg, anti-HBs, total anti-HBc) and hepatitis C screening of all adults at least once and during every pregnancy.
Mycoplasma genitalium causes persistent cervicitis and PID; CDC's resistance-guided regimen is doxycycline for 7 days followed by moxifloxacin 400 mg daily for 7 days.
Pubic lice are treated with permethrin 1% cream rinse and scabies with permethrin 5% cream (ivermectin is an alternative outside pregnancy), plus decontamination of bedding and treatment of close contacts.
HIV Screening
- USPSTF (grade A): Screen everyone aged 15–65 at least once, younger and older people at increased risk, and every pregnant person. CDC recommends opt-out screening for ages 13–64.
- Test: A laboratory 4th-generation HIV-1/2 antigen/antibody immunoassay, followed by a differentiation assay; a reactive screen with a negative differentiation result needs HIV-1 RNA testing to detect acute infection.
- Window period: Most antigen/antibody assays detect infection about 18–45 days after exposure; nucleic acid tests detect it sooner.
- Rescreen at least annually with ongoing risk and repeat in the third trimester for pregnant people at risk or in high-incidence areas.
HIV Pre-Exposure Prophylaxis (PrEP)
The USPSTF (2023, grade A) recommends offering PrEP to anyone at increased risk, such as a partner with HIV whose viral load is not suppressed, inconsistent condom use with partners of unknown status, a recent bacterial STI, or injection drug use.
| Agent | Dosing | Key Points for Women |
|---|---|---|
| TDF/FTC (oral) | One tablet daily | Approved for all exposures; daily dosing reaches maximal cervicovaginal tissue levels after about 20–21 days (about 7 days for rectal tissue); check creatinine and hepatitis B status because stopping it can flare HBV |
| TAF/FTC (oral) | One tablet daily | Not approved for people exposed through receptive vaginal sex |
| Cabotegravir (CAB-LA) | IM injections at 0 and 1 month, then every 2 months | Superior to oral PrEP in trials of cisgender women; needs an HIV RNA test before each injection |
| Lenacapavir | Subcutaneous injections every 6 months after an oral loading phase | FDA-approved June 2025; 100% efficacy among cisgender women in PURPOSE 1; CDC now recommends it as a PrEP option |
Before any PrEP, document a negative HIV test and screen for STIs every 3 months (oral) or at injection visits. TDF/FTC is considered safe during conception, pregnancy, and breastfeeding, so PrEP should continue if an at-risk patient becomes pregnant.
Post-Exposure Prophylaxis (nPEP)
Start a 28-day, 3-drug regimen as soon as possible and no later than 72 hours after a high-risk exposure. CDC's 2025 update prefers single-tablet bictegravir/emtricitabine/tenofovir alafenamide. Transition directly to PrEP at the end of PEP if risk continues.
Doxycycline PEP: Not for Cisgender Women
CDC's 2024 guidance recommends doxycycline 200 mg within 72 hours after condomless sex to prevent syphilis, gonorrhea, and chlamydia only for men who have sex with men and transgender women with a bacterial STI in the past year. A trial among cisgender women in Kenya showed no benefit, so doxy-PEP is not recommended for cisgender women.
Hepatitis B
- Screening (CDC 2023): Test every adult at least once with the triple panel (HBsAg, anti-HBs, total anti-HBc), and every pregnancy with HBsAg.
- Vaccination: Universal for adults aged 19–59; for those 60 and older with risk factors or on request.
| HBsAg | Anti-HBc (total) | Anti-HBs | Interpretation |
|---|---|---|---|
| Negative | Negative | Positive | Immune from vaccination |
| Negative | Positive | Positive | Immune from resolved natural infection |
| Positive | Positive (IgM) | Negative | Acute infection |
| Positive | Positive (IgG) | Negative | Chronic infection (HBsAg >6 months) |
| Negative | Negative | Negative | Susceptible: vaccinate |
| Negative | Positive | Negative | Isolated core antibody: resolved infection, window period, or false positive; check HBV DNA |
Chronic infection needs HBV DNA, liver tests, referral, and hepatocellular carcinoma surveillance when indicated. In pregnancy, tenofovir from 28–32 weeks lowers transmission when HBV DNA exceeds 200,000 IU/mL, and the newborn gets HBIG plus vaccine within 12 hours.
Hepatitis C
- Screening (CDC 2020): All adults 18 and older at least once, every pregnancy, and periodically with ongoing risk such as injection drug use.
- A reactive antibody test needs HCV RNA to confirm current infection; antibody persists after cure or spontaneous clearance.
- Direct-acting antivirals (8–12 weeks) cure more than 95%. Sexual transmission is uncommon but rises with HIV coinfection and traumatic sexual practices.
Mycoplasma genitalium
A cause of persistent or recurrent cervicitis, urethritis, and some PID. Test with NAAT when cervicitis persists after standard therapy; routine screening of asymptomatic women is not recommended. Because macrolide resistance is common, CDC's 2021 regimen is doxycycline 100 mg twice daily for 7 days, then moxifloxacin 400 mg daily for 7 days. If resistance testing shows macrolide sensitivity, doxycycline is followed by azithromycin (1 g, then 500 mg daily for 3 days).
Ectoparasites and Molluscum
| Condition | Presentation | Treatment |
|---|---|---|
| Pubic lice (Pthirus pubis) | Pubic itching, visible lice and nits on hair shafts | Permethrin 1% cream rinse, washed off after 10 minutes; retreat in 7–10 days if needed; launder bedding at high heat; treat partners within the past month |
| Scabies (Sarcoptes scabiei) | Intense nocturnal itching, burrows in web spaces, wrists, waistline, and genitals | Permethrin 5% cream neck to toes, washed off after 8–14 hours, repeat in 1–2 weeks; oral ivermectin 200 mcg/kg repeated in 14 days is an alternative but is avoided in pregnancy; itching can persist 2 weeks after cure |
| Molluscum contagiosum | Firm, dome-shaped, umbilicated papules on the genitals or thighs in adults | Self-limited; cryotherapy or curettage; extensive lesions should prompt HIV testing |
A 26-year-old cisgender woman whose male partner has HIV with a detectable viral load requests pre-exposure prophylaxis. She has receptive vaginal intercourse and has normal renal function. Which PrEP option is NOT appropriate for her?
Daily oral tenofovir disoproxil fumarate/emtricitabine (TDF/FTC)
Injectable cabotegravir every 2 months after initiation doses
Daily oral tenofovir alafenamide/emtricitabine (TAF/FTC)
Subcutaneous lenacapavir every 6 months
A 35-year-old woman has hepatitis B screening with these results: HBsAg negative, total anti-HBc positive, and anti-HBs positive. She has never received hepatitis B vaccine. How should these results be interpreted?
Immunity from a resolved past natural infection
Immunity from prior vaccination
Chronic hepatitis B infection requiring antiviral therapy
Acute hepatitis B infection in the window period
A 24-year-old woman has persistent mucopurulent cervicitis 4 weeks after completing CDC-recommended treatment for chlamydia, with negative repeat gonorrhea and chlamydia NAATs. A Mycoplasma genitalium NAAT is positive, and resistance testing is unavailable. What is the recommended treatment?
Azithromycin 1 g orally in a single dose, repeated in 1 week
Ceftriaxone 500 mg IM in a single dose plus a test of cure in 4 weeks
Metronidazole 500 mg orally twice daily for 7 days plus partner treatment
Doxycycline for 7 days, then moxifloxacin 400 mg daily for 7 days
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