Which patients who meet criteria for a HEPA‑filtered positive‑pressure protective‑environment (e.g., allogeneic stem‑cell transplant recipients or those with prolonged severe neutropenia) are excluded from such rooms?

Patients Excluded from HEPA-Filtered Protective Environments

Absolute Contraindication: Active Airborne Infectious Disease

Patients with active airborne infectious diseases—including tuberculosis, measles, varicella-zoster virus (chickenpox), disseminated herpes zoster, or smallpox—are strictly forbidden from placement in protective environments, even when they meet criteria for immunocompromised isolation. 1

Rationale for Exclusion

• Protective environments (PE) maintain positive air pressure relative to corridors, meaning air flows outward from the patient room into adjacent spaces. 1
• This design is the opposite of airborne infection isolation (AII) rooms, which require negative pressure to contain infectious particles within the room. 1
• Placing a patient with active airborne infection in a positive-pressure PE would aerosolize infectious particles throughout the unit, exposing other severely immunocompromised patients to life-threatening pathogens. 1

Specific Infectious Contraindications

• Active pulmonary or laryngeal tuberculosis requires negative-pressure AII rooms with ≥12 air changes per hour (ACH) and air exhausted to the outside or HEPA-filtered before recirculation. 1
• Disseminated herpes zoster (regardless of immune status) mandates airborne and contact precautions in negative-pressure rooms until all lesions are dried and crusted. 2
• Localized herpes zoster in immunocompromised patients requires airborne precautions in negative-pressure isolation until disseminated infection is ruled out, as these patients experience prolonged viral shedding. 2
• Measles or varicella (chickenpox) in any patient necessitates negative-pressure AII rooms, as these infections spread readily via airborne droplet nuclei <5 µm in diameter. 1

Common Clinical Pitfall

• Do not confuse protective environments (positive pressure for immunocompromised hosts) with airborne infection isolation rooms (negative pressure for infectious patients)—they serve opposite purposes and are mutually exclusive. 1, 3
• A severely neutropenic allogeneic HSCT recipient who develops active tuberculosis or disseminated zoster must be transferred immediately from the PE to a negative-pressure AII room, despite ongoing immunosuppression. 1, 2

Patients Who Appropriately Remain in Standard Rooms

While not "forbidden" from PE, the following immunocompromised patients do not require HEPA-filtered positive-pressure rooms and should be managed in standard hospital rooms with routine infection-prevention measures:

• Autologous HSCT recipients without prolonged neutropenia (ANC >500 cells/mm³ or neutropenia <14 days) have lower infection risk than allogeneic recipients and do not need specialized ventilation. 1, 3, 4
• Solid-organ transplant recipients (heart, liver, lung, kidney) lack sufficient evidence to mandate PE placement; no recommendation exists for routine use. 1
• Patients receiving standard (non-intensive) chemotherapy regimens with brief neutropenia (<7 days) can be managed in ordinary single-patient rooms with standard barrier precautions. 3
• HIV-infected patients, diabetics, and those on chronic steroids without severe prolonged neutropenia (ANC <500 cells/mm³ for >14 days) do not meet high-risk criteria for PE. 1

Technical Distinction Between Room Types

Feature	Protective Environment (PE)	Airborne Infection Isolation (AII)
Pressure	Positive (+2.5 Pa relative to corridor) [1]	Negative (air flows inward) [1]
Air flow direction	Outward from room to corridor [1]	Inward from corridor to room [1]
Purpose	Protect immunocompromised patient from environmental pathogens [1]	Contain infectious particles from spreading to others [1]
Patient population	Allogeneic HSCT, severe prolonged neutropenia [1,3]	Active TB, measles, varicella, disseminated zoster [1,2]
HEPA filtration	Incoming air filtered [1]	Exhaust air filtered (if recirculated) [1]

Algorithm for Room Assignment

1. Does the patient have active airborne infectious disease?

   • Yes → Negative-pressure AII room required, PE contraindicated 1, 2
   • No → Proceed to step 2

2. Is the patient an allogeneic HSCT recipient?

   • Yes → Mandatory PE placement (positive pressure, HEPA, ≥12 ACH) 1, 3
   • No → Proceed to step 3

3. Does the patient have severe prolonged neutropenia (ANC <500 cells/mm³ for >14 days or <100 cells/mm³ for 1 week)?

   • Yes → Consider PE, especially during construction/renovation 1, 3
   • No → Standard single-patient room with routine precautions 3