Can air purifiers with High Efficiency Particulate Air (HEPA) filters be used in an infectious ward to prevent airborne transmission in immunocompromised patients?

HEPA Air Purifiers in Infectious Wards for Immunocompromised Patients

Yes, HEPA air purifiers can and should be used in infectious wards to protect immunocompromised patients, but only as a supplemental measure to proper ventilation systems, not as a replacement. 1

Primary Guideline Recommendations

When HEPA Filtration is Indicated

The CDC explicitly recommends HEPA filtration for immunocompromised patients in protective environments (PE rooms), which require:

• Positive pressure of +2.5 to +8 Pa relative to corridors 1
• ≥12 air changes per hour (ACH) for new construction 1
• HEPA filters with 99.97% efficiency for particles ≥0.3 µm 1
• Air directed toward the patient then eliminated 1

Acceptable Applications in Infectious Wards

HEPA filters can be deployed in multiple configurations according to CDC guidelines:

• Fixed recirculation systems mounted in ceilings or walls for individual room air cleaning 1
• Portable air cleaners as supplemental devices 1
• Exhaust duct filtration before air recirculation 1

Critical Implementation Requirements

Installation and Maintenance Standards

HEPA filters must be installed carefully and maintained meticulously to ensure adequate function 1. The CDC emphasizes that:

• Manufacturers must provide documentation of both HEPA filter efficiency AND the device's efficiency in lowering room air contaminant levels 1
• Facilities must have ventilation engineering expertise available, either on staff or through consultation 1
• Monthly verification of proper function is required 1

Effectiveness Evidence

HEPA filters can be expected to remove infectious droplet nuclei from contaminated air because:

• M. tuberculosis droplet nuclei range from 1-5 µm in diameter, similar to Aspergillus spores (1.5-6 µm) 1
• HEPA filters have proven effectiveness reducing Aspergillus spores to below measurable levels 1
• Recent research demonstrated 85.38% removal of infectious SARS-CoV-2 at 1 ventilation volume, 96.03% at 2 volumes, and >99.97% at 7.1 volumes 2
• A hospital study showed portable HEPA filters reduced invasive aspergillosis incidence from 34.61 to 17.51 per 100,000 patient-days (incidence rate ratio 1.98, p=0.01) 3

Important Limitations and Caveats

Portable Units Have Significant Constraints

The CDC explicitly states that the effectiveness of portable HEPA room-air cleaning units has not been evaluated adequately, and there is probably considerable variation in their effectiveness 1. Therefore:

• Portable units should only be used as temporary emergency measures while fixed systems are restored or upgraded 4
• Engineering consultation is mandatory to determine proper placement and ensure adequate ACH 4
• Fixed recirculation systems are preferred over portable units due to greater reliability in achieving adequate room air mixing and airflow patterns 5

Not a Replacement for Primary Controls

HEPA filtration supplements but does not replace other infection control measures:

• Personal respiratory protection (N95 respirators) remains mandatory for staff entering rooms with TB or airborne viral disease patients 1, 6
• Proper negative pressure isolation rooms are still required for infectious patients (not the same as positive pressure PE rooms for immunocompromised patients) 1
• Administrative controls, source control, and proper ventilation design remain the foundation of airborne infection control 1

Device Selection Criteria

Avoid devices that lose filtration efficiency below 99.97% if electrostatic components fail 1. Such devices:

• Should not be used in systems recirculating air from TB isolation or treatment rooms back into general facility ventilation 1
• Must maintain passive HEPA filtration as the primary mechanism 1

Specific Populations and Settings

High-Risk Immunocompromised Patients

Patients requiring protective environments include:

• Allogeneic hematopoietic stem cell transplant recipients 1
• Severely neutropenic patients (ANC <500 cells/mL) for prolonged periods 1
• Patients receiving intensive chemotherapy (e.g., childhood acute myelogenous leukemia) 1

Areas Requiring HEPA Filtration

Beyond individual patient rooms, HEPA filtration should be considered for:

• General-use areas in facilities serving high TB prevalence populations (waiting rooms, emergency departments, radiology suites) 1
• Operating theatres for immunocompromised patients (requiring ≥40 ACH with unidirectional flow or ≥20 ACH with turbulent flow) 1
• ICUs and burn units caring for high-risk patients 1

Common Pitfalls to Avoid

Do not disrupt controlled airflow patterns - Improper placement of portable units can compromise rather than enhance air quality by disrupting directional airflow from clean to less-clean areas 4, 6

Do not rely solely on air purifiers for droplet-transmitted infections - Most respiratory infections spread primarily through large droplets and direct/indirect contact, limiting the effectiveness of air purifiers for these pathogens 7, 5

Do not use air purifiers as justification to reduce other infection control measures - HEPA filtration is an adjunct, not a substitute for proper isolation precautions, PPE, and administrative controls 1, 6