Overview of tight fit and infection prevention benefits of respirators (filtering face pieces)

Abstract

Regulations for measures to protect against SARS-CoV-2 transmission vary widely around the world, with very strict regulations in Germany where respirators (filtering face piece FFP2 or comparable) are often mandatory. The efficiency of respirators, however, depends essentially on the tight facial fit avoiding the bypass of contaminated air via gaps between mask and wearer's face. The facial fit can be verified in a fit test. The aim of this review was to describe the quantitative fit test results depending on the respirator designs. A literature search revealed 29 suitable studies. Of all respirators with circumferential head straps, three-panel folded dome-shaped respirators showed the best fit (80.8% of 4625 fit tests passed), followed by rigid-dome-shaped respirators (72.4% of 8234 fit tests passed), duckbill-shaped respirators (31.6% of 2120 fit tests passed), and coffee-filter-shaped respirators (30.9% of 3392 fit tests passed). Respirators with ear loops showed very poor tight fit (3.6% of 222 fit tests passed). In four randomized control trials, single-use respirators were not shown to be superior to surgical masks for the prevention of laboratory-confirmed viral respiratory infections, even when adjusted with a fit test. Therefore, we consider the mandatory use of respirators to be disproportionate and not supported by evidence. Further evidence should be generated, in which scenarios respirators might provide an effective benefit as part of occupational health and safety. For situations with confirmed benefits, only high-quality disposable respirators with head straps or respiratory protective equipment of higher protective levels should be used.

Keywords: Fit test; Prevention; Respirator; Viral respiratory tract infection.

Figure 1

Exemplary shape types of disposable respirators. Dome-shaped respirators, which are rigidly preformed (A) or three-panel folded (B, C, H), as well as respirators consisting of two folded planes in which the fold seam runs horizontally (duckbill shape, D, E) or vertically (coffee filter shape, F, G, I, J) are displayed. The respirators can be fixed to the head of the person wearing them with head straps (A–G) or ear loops (H–J). In the case of head straps, one single head strap can be movably deflected at the edges of the mask (A, D, E, F) or head straps of different lengths are attached (B, C, G). For respirators with ear loops, technical aids can be used to connect the ear loops behind the head (H, I). Another important distinguishing criterion is the presence of an exhalation valve (B, D, F).

Figure 2

Flow charts illustrating the search strategies for the review. The search strategies for evaluating quantitative fit tests (A) and for randomized control trials comparing medical masks and FFP masks (B) are displayed.