Persistence of SARS-CoV-2 on N95 filtering facepiece respirators: implications for reuse
Updated July 23, 2024
July 2024
NIOSH Dataset RD-1088-2024-0
Introduction
In response to the shortage of N95® filtering facepiece respirators (FFRs) for healthcare workers during the COVID-19 pandemic, the Centers for Disease Control and Prevention (CDC) issued strategies for extended use and limited reuse of N95 FFRs to conserve supply. Previously worn N95 FFRs can serve as a source of pathogens, which can be transferred to the wearer while doffing and donning a respirator when practicing reuse. To reduce the risk of self-contamination when donning and doffing reused FFRs, the CDC suggested storing FFRs for five days between uses to allow for the decay of viable pathogens including SARS-CoV-2. This study assessed the persistence of the SARS-CoV-2 strain USA-WA1/2020 on N95 FFRs under controlled storage conditions for up to five days to inform the CDC guidance.
Methods Collection
Virus propagation
- Virus used: Severe Acute Respiratory Syndrome (SARS)-Coronavirus CoV-2 strain USA-WA1/2020 (WA1), obtained from BEI Resources (Manassas, VA).
- Working stocks had titers of approximately 106 tissue-culture infectious doses 50% [TCID50] per milliliter.
- Material stored as single-use vials at ≤ -80⁰
Test coupons
- Six NIOSH Approved® FFR models
- Four NIOSH Approved and FDA-cleared Surgical N95 FFRs
- 3M 1860 and VFlex 1804
- Moldex 1512 and 2200
- Two NIOSH Approved N95 FFRs
- 3M 8210 and 8511
- Non-porous controls – glass coupons (microscope cover slides)
- Rectangular coupons (2×5 cm) taken from unused FFRs.
- Four NIOSH Approved and FDA-cleared Surgical N95 FFRs
Coupon contamination and storage conditions
- Virus suspended in
- Complete cell culture medium
- Human saliva
- Ten droplets (10 µL each droplet) applied to coupons under ambient conditions (20⁰C–22⁰C and 30%–50% RH).
- Total deposition of SARS-CoV-2 was approximately 1×105 TCID50 across the outer surface of the FFR coupon.
- Coupons were allowed to dry under ambient conditions.
- Transferred to brown paper bags and stored at 20⁰C–22⁰C and at 20% (15%–25%), 45% (30%–50%), and 75% (70%–75%) RH.
- Virus on the FFR coupons and glass slides were extracted after 0- , 1- , 24- , 48- , 96- , and 120-hr timepoints.
- Additional assessments were performed after 4- , 6- , and 12-hr post-drying when more data points were needed.
- Virus persistence was evaluated in triplicate for each tested surface, timepoint, and condition.
- Some conditions were not tested for all FFR models due to limited supply.
Virus extraction and analysis
- Coupons were removed from the paper bags and placed into individual 50-mL conical tubes containing a 10-mL extraction buffer.
- Starting volume was concentrated to approximately 0.5 mL.
- Media was added to equilibrate all washed retentates to approximately 2 mL.
- Virus viability was assessed by TCID50 assay in Vero E6 cells.
- Samples inoculated in quintuplicate onto a single 96-well plate at 70% cell monolayer confluency.
- Plates were incubated at 37 ± 2⁰C and 5 ± 2% carbon dioxide for 72 ± 4 hr.
- Observed microscopically for cytopathic effects (CPE, visible morphological changes in cell cultures caused by viral infections).
- Used to quantitatively calculate the viral titer for each sample.
- Extraction efficiency was assessed relative to a direct spiking and quantification of the extraction medium for
- NIOSH Approved and FDA-cleared surgical N95 FFR (3M 1860)
- NIOSH Approved N95 FFR (3M 8511)
- Glass control surface
Citations – Publications based on this dataset:
Fisher EM; Kuhlman MR; Choi YW; Jordan TL; Sunderman M. Persistence of SARS-Co-V-2 on N95 filtering facepiece respirators: implications for reuse. J Occup Environ Hyg 2021 Dec; 18(12):570-578, DOI: 10.1080/15459624.2021.1985727.
Acknowledgements
This work was supported by the Centers for Disease Control and Prevention’s (CDC) National Institute for Occupational Safety and Health (NIOSH).
Edward M. Fisher, efisher@cdc.gov
Michael R. Kuhlman, kuhlmanm@battelle.org
Young W. Choi, choiy@battelle.org
Traci L. Jordan, jordant@battelle.org
Michelle Sunderman, sunderman@battelle.org
Contact
For further information contact:
Research Branch (RB)
National Personal Protective Technology Laboratory (NPPTL)
National Institute for Occupational Safety and Health (NIOSH)
626 Cochrans Mill Road
Pittsburgh, PA 15236
ODAdmin@cdc.gov