ICU Infections in HIV/AIDS Patients

CD4 Count as the Roadmap

1. Respiratory Infections (Most Common ICU Admission Cause)

Pneumocystis jirovecii Pneumonia (PCP)

• Most common OI leading to ICU admission in HIV patients
• Occurs almost exclusively at CD4 <200 cells/μL
• Presents with: subacute progressive dyspnea, dry cough, fever, hypoxemia
• CXR/CT: bilateral interstitial thickening and ground-glass opacities (bilateral, perihilar, classically "bat-wing" pattern); may also form pneumatoceles (thin-walled cysts) which can rupture causing pneumothorax
• Diagnosis: BAL with silver or Giemsa stain, immunofluorescence, or PCR
• Treatment: TMP-SMX (first-line) x 21 days; for severe PCP (PaO2 <70 mmHg), add adjunctive corticosteroids (prednisone 40 mg BD → taper)
• Recent RCT in Lancet Respiratory Medicine 2025 examined adjunctive corticosteroids specifically in non-AIDS patients with severe PCP - benefit appears steroid class-specific to the AIDS population per established evidence

Bacterial Pneumonia

• Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus (including MRSA), Pseudomonas aeruginosa (at low CD4)
• Recurrent bacterial pneumonia (>1 episode/year) is itself an AIDS-defining illness
• Higher risk of bacteremia compared to immunocompetent hosts

Tuberculosis (TB)

• Can occur at any CD4 count but dissemination is more likely at CD4 <200
• May present atypically: lower lobe involvement, hilar adenopathy, miliary pattern
• Miliary TB frequently causes ICU-level respiratory failure
• Key concern: drug interactions between rifampicin and antiretrovirals (especially PIs, NNRTIs)

2. CNS Infections

Cryptococcal Meningitis

• Caused by Cryptococcus neoformans - the most common life-threatening fungal infection in HIV patients; AIDS-defining illness in 40-60% of patients when diagnosed with AIDS
• Typically CD4 <100 cells/μL
• Presentation: subacute headache, fever, meningism often absent; altered consciousness if elevated ICP
• Diagnosis: India ink stain, serum/CSF cryptococcal antigen (CrAg), CSF culture
• ICP management is critical: therapeutic LPs or lumbar drain if opening pressure >25 cmH2O
• Treatment: Amphotericin B deoxycholate + flucytosine (induction 2 weeks) → fluconazole consolidation → maintenance
• Pathophysiology: polysaccharide capsule prevents phagocytosis, impairs macrophage antigen presentation, depletes complement, reduces leukocyte migration - Murray & Nadel's, p. 2648

Cerebral Toxoplasmosis

• Toxoplasma gondii reactivation at CD4 <100 cells/μL
• Presents with focal neurologic deficits, fever, seizures, altered consciousness
• CT/MRI: multiple ring-enhancing lesions (basal ganglia, corticomedullary junction), surrounding edema
• Treatment: Pyrimethamine + sulfadiazine + leucovorin (first-line); alternative pyrimethamine + clindamycin
• Maintenance therapy required until CD4 >200 cells/μL for >6 months (Adams and Victor's Neurology)

CMV Encephalitis/Meningitis

• Occurs at CD4 <50 cells/μL
• ICU intensivists should be aware: CMV is an important and often underdiagnosed pathogen in immunocompromised ICU patients (Fernandez et al., Intensive Care Med 2025)
• Treatment: Ganciclovir or foscarnet

Progressive Multifocal Leukoencephalopathy (PML)

• JC virus reactivation, CD4 <200
• Subacute demyelinating process - no effective direct treatment; ART initiation is cornerstone

3. Systemic/Bloodstream Infections

Sepsis from Bacterial Pathogens

• Recurrent Salmonella septicemia is an AIDS-defining illness
• Staphylococcus aureus bacteremia (especially MRSA) - higher in IV drug users
• Gram-negative bacteremia from enteric organisms (at lower CD4)
• Encapsulated organisms: S. pneumoniae, H. influenzae (functional hyposplenism)

Disseminated MAC (Mycobacterium avium Complex)

• Almost exclusively CD4 <50 cells/μL
• Presents with: fever, night sweats, weight loss, hepatosplenomegaly, pancytopenia
• ICU implications: can cause severe anemia, cytopenias requiring transfusion
• Treatment: Clarithromycin + ethambutol (± rifabutin)
• ART now prioritized over prophylaxis per updated 2024 NIH/IDSA guidelines

Disseminated Fungal Infections

• Histoplasma capsulatum - endemic in central/south-central US; disseminates to ICU-level disease at low CD4
• Candida - candidemia in the setting of indwelling catheters, broad-spectrum antibiotics, HIV
• Aspergillus - invasive pulmonary aspergillosis, primarily when CD4 very low or with neutropenia

4. Unique ICU Considerations in HIV Patients

Immune Reconstitution Inflammatory Syndrome (IRIS)

• Occurs when ART is started in the setting of untreated OI
• Paradoxical worsening as immune function returns
• Particularly dangerous with cryptococcal meningitis (rapidly elevated ICP) and TB
• Manage with corticosteroids in severe cases; do not stop ART unless life-threatening

When to Start ART in the ICU

• For most OIs: start ART within 2 weeks of OI treatment
• Exception: Cryptococcal meningitis - delay ART 4-6 weeks to reduce IRIS-related mortality
• Exception: TB meningitis - delay 4-8 weeks

Distinguishing OI from Non-OI Infections

• What is the CD4 count? (rules in/out OI spectrum)
• Is the patient on ART? What is the viral load?
• Has OI prophylaxis (TMP-SMX, azithromycin, fluconazole) been given?

Drug Interactions

• Rifampicin dramatically reduces PI and NNRTI levels - use rifabutin instead if possible
• Fluconazole inhibits CYP3A4 - watch for toxicity with many antiretrovirals
• TMP-SMX can cause hyperkalemia, elevated creatinine (inhibits tubular secretion) - not true AKI

5. Prophylaxis Summary (NIH/IDSA/HIVMA 2024 Guidelines)

Summary: Approach to an HIV Patient with Infection in the ICU

1. Determine CD4 count - this stratifies the entire differential
2. Check ART status and viral load - undetectable viral load on ART makes most OIs less likely
3. Obtain broad workup early: blood cultures, CrAg (serum), BAL, LP if CNS features, CMV PCR, TB workup
4. Empirically cover PCP if hypoxic + CD4 <200 (TMP-SMX + steroids if severe)
5. Empirically cover bacterial sepsis with broad-spectrum antibiotics while awaiting cultures
6. Beware of IRIS if starting ART during active OI
7. Involve infectious disease early for ART timing, drug interactions, and OI-specific management