AUTHOR=Rodriguez-Palacios Alex , Conger Mathew , Cominelli Fabio 

TITLE=Germ-Free Mice Under Two-Layer Textiles Are Fully Protected From Bacteria in Sprayed Microdroplets: A Functional in vivo Test Method of Facemask/Filtration Materials

JOURNAL=Frontiers in Medicine

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2020.00504

DOI=10.3389/fmed.2020.00504

ISSN=2296-858X

ABSTRACT=<p>Several studies have measured the effectiveness of masks at retaining particles of various sizes <italic>in vitro</italic>. To identify a functional <italic>in vivo</italic> model, herein we used germ-free (GF) mice to test the effectiveness of textiles as filtration material and droplet barriers to complement available <italic>in vitro</italic>-based knowledge. Herein, we report a study conducted <italic>in vivo</italic> with bacteria-carrying microdroplets to determine to what extent household textiles prevent contamination of GF mice in their environment. Using a recently validated spray-simulation method (mimicking a sneeze), herein we first determined that combed-cotton textiles used as two-layer-barriers covering the mouse cages prevented the contamination of all GF animals when sprayed 10–20 bacterial-droplet units/cm<sup>2</sup>. In additional to exposure trials, the model showed that GF mice were again protected by the combed-cotton textile after the acute exposure to 10 times more droplets (20 “spray-sneezes”, ~200 bacterial-droplet units/cm<sup>2</sup>). Overall, two-layer combed-cotton protected 100% of the GF mice from bacteria-carrying droplets (<italic>n</italic> = 20 exposure-events), which was significantly superior compared to 100% mouse contamination without textile coverage or when 95% partly covered (<italic>n</italic> = 18, Fisher-exact, <italic>p</italic> &lt; 0.0001). Of relevance is that two different densities of cotton were equally effective (100%) in preventing contamination regardless of density (120–vs. 200 g/m<sup>2</sup>; <italic>T</italic>-test, <italic>p</italic> = 0.0028), suggesting that similar density materials could prevent droplet contamination. As a practical message, we conducted a speech trial (counting numbers, 1–100) with/without the protection of the same cotton textile used as face cover. The trial illustrated that contamination of surfaces occurs at a rate of &gt;2–6 bacteria-carrying saliva-droplets per word (2.6 droplets/cm<sup>2</sup>, 30 cm) when speaking at 60–70 decibels and that cotton face covers fully prevent bacterial surface contamination.</p>