How does data on virus viability on surfaces apply to re-use of masks, storage conditions and timeframe?
Experimental studies have indicated that SARS-CoV-2 can remain viable for hours in the air, up to 24 hours on cardboard, and for 2-3 days on plastic and stainless steel. While the rapidity of drying of the mucous particles carrying the virus seems to be the major factor in viability, this quantitative data is not directly applicable to real-life situations where variations in temperature, humidity, and UV radiation can significantly decrease viral viability.
The recommendation to store respirators for 5 days between use (if no disinfectants are used) is a precautionary recommendation allowing for maximum safety in re-use of masks that may have had significant viral contamination. Storage in a paper bag (as opposed to plastic) will allow for better drying conditions, and prevent moisture-facilitated mold overgrowth.
van Doremalen N, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. NEJM 2020;383:1564-1567. Accessed May 6, 2020 at: https://www.nejm.org/doi/full/10.1056/NEJMc2004973