Respiratory source control versus receiver protection: impact of facemask fit

Placing a surgical mask on an infected patient (respiratory source control) may offer a health-care worker (HCW) more protection than donning an N95 respirator (receiver protection). This observation was made in an in vitro study that used hard, nondeformable faces, and the lack of proper N95 fit may have accounted for the observed results. In the present study, we test the effects of fit on respiratory source control protection, using a soft, deformable mannequin head.

Resusci Anne CPR mannequin heads were placed in a chamber allowing 6 air exchanges/hr (14 cubic feet per minute), to simulate an infected patient (source) and an HCW (receiver). The heads were ventilated with a tidal breathing pattern. The source exhaled radioactive aerosols, and a filter was attached to the receiver to quantify inhaled exposure. N95 respirators and surgical masks were tested on both heads. The degree of protection was expressed by calculating the reduction in exposure expressed as a simulated workplace protection factor (sWPF; the ratio of exposure with mask to exposure without mask) compared statistically using confidence intervals.

Use of the Resusci Anne heads resulted in improved fit, with higher sWPF than previously reported, for example, for source N95 mask combinations (7,174 vs. 317) as well as receiver (7.53 vs. 1.37). Masks placed on the receiver provided minimal exposure protection (sWPF range 0.99-7.53), except when sealed with Vaseline (sWPF 63.1). Any mask applied to the source mannequin resulted in significant reductions in exposure (sWPF range 214-17,038).

Improved fit significantly enhanced the effects of source control protection. A Vaseline-sealed N95 respirator on the receiver offered less protection when compared with any mask on the source. Respiratory source control can offer more protection to HCW and potentially decrease the spread of aerosolized infections.