Thermal Disinfection Inactivates SARS-CoV-2 in N95 Respirators while Maintaining Their Protective Function

Daeschler, S. C.; Manson, N.; Joachim, K.; Chin, A. W. H.; Chan, K.; Chen, P. Z.; Tajdaran, K.; Mirmoeini, K.; Zhang, J. J.; Maynes, J. T.; Science, M.; Darbandi, A.; Stephens, D.; Poon, L. L. M.; Gu, F.; Borschel, G. H.

Background: The unprecedented demand and consequent global shortage of N95 respirators during the COVID-19 pandemic have left frontline workers vulnerable to infection. To expand the supply, we validated a rapidly applicable low-cost decontamination protocol in compliance with US-regulatory guidelines to enable the safe reuse of personalized, disposable N95-respirators. Methods: Four common models of N95-respirators were disinfected for 60 minutes at {degrees}C either at 0% or 50% relative humidity (RH). Effective inactivation of SARS-CoV-2 and E. coli was evaluated in inoculated masks. The N95 filter integrity was examined with scanning electron microscopy. The protective function of disinfected N95 respirators was tested against US NIOSH standards for particle filtration efficiency, breathing resistance and respirator fit. Results: A single heat treatment inactivated SARS-CoV-2 (undetectable, detection limit: 100 TCID50/ml) and E. coli (0 colonies at 50%RH) in all four respirator models. Even N95-respirators that underwent ten dry heat, or up to five 50%RH-controlled decontamination cycles maintained their integrity and met US-governmental criteria for approval regarding fit (10x dry heat: 194.48 {+/-} 15.5; 99%CI: 185.5 to 203.5; 5x at 50%RH: 198.2 {+/-} 6.3; 99%CI: 189.4 to 207; n=23 each, pass value [≥] 100,), breathing resistance (10x dry heat: 68.0 {+/-} 8.4 Pa, 99%CI: 61.8 to 74.1, n=16; 5x at 50%RH: 78.5 {+/-} 19.7 Pa, 99%CI: 21 to 135.9, n=4, pass value [≤] 343.23Pa), and filtration levels (10x dry heat: 97.6 {+/-} 1.1%, 99%CI: 96.8 to 98.4; n=16; 5x at 50%RH: 97.18 {+/-} 0.49, 99%CI: 95.7 to 98.6, n=4, pass value [≥] 95 %). Interpretation: This rapid process enables large-scale decontamination of existing N95-respirators using commonly sourced equipment during the COVID-19 pandemic.