Respirator Testing Using Virus Aerosol: Comparison between Viability Penetration and Physical Penetration

Area of Science:

• Environmental microbiology
• Filter science
• Respiratory protection technology

Background:

• Assessing respirator filter efficacy against viral aerosols is crucial for public health.
• Current testing methods may not fully correlate physical particle penetration with biological viral inactivation or penetration.
• Understanding these correlations is key to improving respirator performance standards.

Purpose of the Study:

• To compare the penetration of viable MS2 bacteriophage, viral RNA, and physical particles (by volume and number) through respirator filter media.
• To evaluate the correlation between different penetration metrics and actual viral viability.
• To assess the suitability of the current photometer-based test method for evaluating respirator performance against virus aerosols.

Main Methods:

• MS2 bacteriophage aerosols were generated and passed through filter media from three respirator models.
• Viability, viral RNA, particle volume (fluorescence), particle number, and photometric penetration were measured.
• Upstream and downstream aerosol samples were analyzed for virus survival rates.

Main Results:

• Viability and viral RNA penetration were better represented by particle volume penetration than particle number penetration.
• Both viability and viral RNA penetration were several-fold lower than photometric penetration.
• Differences in virus survival between upstream and downstream samples influenced photometric penetration measurements.

Conclusions:

• Photometric penetration can overestimate respirator protection against virus aerosols due to virus survival.
• Particle volume penetration offers a better approximation of viral RNA and viability penetration than particle number.
• The current NIOSH photometer-based test method provides a rapid, albeit rough, differentiation of respirator performance against virus aerosols.