Immunology
HIV & AIDS — Opportunistic Infections
Immunology

HIV & AIDS — Opportunistic Infections

CD4-based prophylaxis + opportunistic infection patterns + ART basics.

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◆Diagnosis & monitoring

  • •Screening: 4th-gen Ag/Ab combo (detects p24 + HIV Ab) — window ~3 weeks
  • •Confirm with HIV-1/2 differentiation immunoassay; HIV RNA viral load if acute
  • •Acute HIV (mono-like illness): screen Ag/Ab negative but HIV RNA positive
  • •Monitor: CD4 count + viral load

◆Prophylaxis by CD4 count

  • •CD4 <200: TMP-SMX for PJP (also covers toxoplasmosis at CD4<100)
  • •CD4 <150 (Ohio/Mississippi valley): itraconazole for histoplasmosis
  • •CD4 <100: TMP-SMX double dose for toxoplasmosis (PJP also covered)
  • •CD4 <50: azithromycin weekly for MAC

◆Opportunistic infections by CD4

  • •<500: Kaposi sarcoma, candida (oral thrush), TB, HSV/zoster, lymphoma
  • •<200: PJP (bilateral interstitial + hypoxia + ↑LDH); HIV-associated dementia
  • •<100: toxoplasmosis (multiple ring-enhancing basal ganglia), cryptococcal meningitis, esophageal Candida
  • •<50: CMV retinitis ('pizza pie' hemorrhages), CMV esophagitis (large linear ulcers), MAC (fever + ↓wt + diarrhea + ↑alk phos), CNS lymphoma (solitary periventricular + EBV in CSF), PML (JC virus)

◆ART basics

  • •Start ART in everyone regardless of CD4
  • •Typical regimen: 2 NRTIs + (INSTI or NNRTI or boosted PI)
  • •Common: tenofovir + emtricitabine + dolutegravir (Biktarvy is bictegravir + emtricitabine + tenofovir alafenamide)
  • •Immune reconstitution inflammatory syndrome (IRIS): worsening with paradoxical inflammation after starting ART; treat both ART + offending infection

◆Special situations

  • •Post-exposure prophylaxis (PEP): 3-drug ART within 72 hr × 28 days (tenofovir/emtricitabine + dolutegravir/raltegravir)
  • •Pre-exposure prophylaxis (PrEP): tenofovir/emtricitabine (Truvada or Descovy) or long-acting cabotegravir
  • •Pregnancy: HIV+ mother → ART throughout + IV zidovudine in labor + ART for infant 6 weeks; avoid breastfeeding in high-resource settings

High-yield pearls

  • ◆Acute HIV: mono-like + negative Ab + positive RNA — high transmission risk
  • ◆Don't forget PEP for occupational AND sexual assault exposure
  • ◆Cryptococcal meningitis: ↑opening pressure → serial LPs; treat amphotericin B + flucytosine then fluconazole
  • ◆Pneumocystis prophylaxis dose < treatment dose
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