A 2300-g (5-lb 1-oz) male newborn is delivered to a 29-year-old primigravid woman. The mother has HIV and received triple antiretroviral therapy during pregnancy. Her HIV viral load was 678 copies/mL 1 week prior to delivery. Labor was uncomplicated. Apgar scores are 7 and 8 at 1 and 5 minutes respectively. Physical examination of the newborn shows no abnormalities. Which of the following is the most appropriate next step in management of this infant?

Administer zidovudine, lamivudine and nevirapine

Administer lamivudine and nevirapine

A 27-year-old G2P1 woman is diagnosed with an HIV infection after undergoing routine prenatal blood work testing. Her estimated gestational age by first-trimester ultrasound is 12 weeks. Her CD4 count is 150 cells/mm^3 and her viral load is 126,000 copies/mL. She denies experiencing any symptoms of HIV infection. Which of the following is appropriate management of this patient's pregnancy?

Avoidance of antibiotic prophylaxis

A 17-year-old girl comes to the urgent care center after testing negative for HIV. She recently had sexual intercourse for the first time and had used a condom with her long-term boyfriend. She has no personal history of serious illness and no history of sexually transmitted infections. However, the patient is still worried about the possibility she has HIV despite the negative HIV test. She states that the package insert of the HIV test shows that of 100 patients who are found to be HIV-positive on PCR, 91 tested positive via the HIV test. Later in the day, a 23-year-old woman with a history of genitourinary chlamydia infection also comes to the urgent care center after testing negative for HIV. She states that she recently had unprotected intercourse with “someone who might have HIV.” If the test is conducted a second time on the 23-year-old patient, how will its performance compare to a second test conducted on the 17-year-old patient?

Decreased negative predictive value

Decreased positive predictive value

A 29-year-old woman tests positive for HIV during pregnancy screening. She is concerned about transmission to her baby. Which of the following interventions most significantly reduces the risk of vertical transmission?

Antiretroviral therapy during pregnancy and labor

A 24-year-old newly immigrated mother arrives to the clinic to discuss breastfeeding options for her newborn child. Her medical history is unclear as she has recently arrived from Sub-Saharan Africa. You tell her that unfortunately she will not be able to breastfeed until further testing is performed. Which of the following infections is an absolute contraindication to breastfeeding?

Human Immunodeficiency Virus (HIV)

A 28-year-old woman G1P0 presents at 38 weeks of gestation for a standard prenatal visit. She endorses occasional mild lower back pain but otherwise remains asymptomatic. Her past medical history is significant for HIV for which she is treated with azidothymidine (AZT). Her vital signs and physical exam are unremarkable. Her current HIV viral titer level is 1,400 copies. If she were to go into labor today, what would be the next and most important step for the prevention of vertical HIV transmission to the newborn?

Urge the patient to have a cesarean section delivery

Add nevirapine to the patient’s AZT

Treat the newborn with AZT following delivery

A 28-year-old G1P0 woman at 16 weeks estimated gestational age presents for prenatal care. Routine prenatal screening tests are performed and reveal a positive HIV antibody test. The patient is extremely concerned about the possible transmission of HIV to her baby and wants to have the baby tested as soon as possible after delivery. Which of the following would be the most appropriate diagnostic test to address this patient’s concern?

Polymerase chain reaction (PCR) for HIV RNA

HIV transmission and epidemiology for USMLE Step 2 CK: High-Yield Microbiology Lessons

HIV Epidemiology - Global Grip, Local Hotspots

Global Burden: Over 38 million people living with HIV worldwide. Highest prevalence in sub-Saharan Africa (e.g., South Africa, Nigeria).
U.S. Epidemiology: Concentrated epidemic with ~1.2 million people.
- Risk Groups: Men who have sex with men (MSM) account for the majority of new diagnoses, followed by heterosexual contact and persons who inject drugs (PWID).
- Disparities: African American and Hispanic/Latino communities are disproportionately affected.
Trends: Global new infections are ↓, but overall prevalence is ↑ due to effective antiretroviral therapy (ART) improving survival.

⭐ High-Yield Fact: In many regions, including the U.S., HIV is a concentrated epidemic. This means it is largely confined to specific key populations, making targeted prevention and testing strategies crucial.

Global HIV Prevalence Cartogram (2015)

Transmission Routes - The Viral Superhighway

Sexual Transmission: Most common route globally. Risk is proportional to the viral load.
- Highest risk: Receptive anal intercourse.
- Other routes (descending risk): Insertive anal, receptive vaginal, insertive vaginal intercourse.
- Co-infection with other STIs (e.g., syphilis, HSV) significantly increases transmission risk by disrupting mucosal integrity.
Parenteral Transmission: Direct inoculation with infected blood.
- IV Drug Use (IVDU): Sharing contaminated needles.
- Occupational Needlestick Injury: Risk is approximately 0.3% per exposure.
- Blood Products/Transfusions: Extremely rare in the US due to rigorous screening (risk < 1 in 2 million).
Vertical (Mother-to-Child) Transmission (MTCT):
- Can occur in utero, during parturition (delivery), or via breastfeeding.
- Baseline risk without intervention: 15-45%.
- With maternal antiretroviral therapy (ART), risk plummets to <1%.

⭐ Undetectable = Untransmittable (U=U): Patients on stable ART with a consistently undetectable viral load do not sexually transmit HIV. This is a critical concept for patient counseling and public health.

Risk & Prevention - Dodging the Danger

Major Transmission Routes:
- Sexual: Receptive anal > insertive anal > receptive vaginal. Genital ulcer disease (e.g., syphilis, HSV) significantly ↑ risk.
- Parenteral: IV drug use > occupational needle-stick (~0.3% risk).
- Vertical: In-utero, peripartum, or breastfeeding. Risk drops to <1% with maternal ART.
Prevention Pillars:
- Biomedical:
  - PrEP (Pre-Exposure Prophylaxis): Daily oral TDF/FTC for high-risk individuals.
  - PEP (Post-Exposure Prophylaxis): 3-drug ART regimen initiated within 72 hours of exposure.
- Treatment as Prevention (TasP).

⭐ U=U (Undetectable = Untransmittable): Individuals with a sustained undetectable viral load on ART cannot sexually transmit the virus to partners.

High‑Yield Points - ⚡ Biggest Takeaways

HIV transmission occurs via sexual contact, parenteral (IV drug use, needle sticks), and vertical (mother-to-child) routes.

Receptive anal intercourse carries the highest sexual transmission risk; blood transfusions are the most efficient mode overall.

Vertical transmission risk plummets to <1% with maternal antiretroviral therapy (ART).

In the U.S., men who have sex with men (MSM) remain the most affected population.

A high viral load directly correlates with increased transmission risk (Undetectable = Untransmittable).

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HIV transmission and epidemiology