Efficacy of Face Shields Against Cough Aerosol Droplets from a Cough Simulator

Abstract

Health care workers are exposed to potentially infectious airborne particles while providing routine care to coughing patients. However, much is not understood about the behavior of these aerosols and the risks they pose. We used a coughing patient simulator and a breathing worker simulator to investigate the exposure of health care workers to cough aerosol droplets, and to examine the efficacy of face shields in reducing this exposure. Our results showed that 0.9% of the initial burst of aerosol from a cough can be inhaled by a worker 46 cm (18 inches) from the patient. During testing of an influenza-laden cough aerosol with a volume median diameter (VMD) of 8.5 μm, wearing a face shield reduced the inhalational exposure of the worker by 96% in the period immediately after a cough. The face shield also reduced the surface contamination of a respirator by 97%. When a smaller cough aerosol was used (VMD = 3.4 μm), the face shield was less effective, blocking only 68% of the cough and 76% of the surface contamination. In the period from 1 to 30 minutes after a cough, during which the aerosol had dispersed throughout the room and larger particles had settled, the face shield reduced aerosol inhalation by only 23%. Increasing the distance between the patient and worker to 183 cm (72 inches) reduced the exposure to influenza that occurred immediately after a cough by 92%. Our results show that health care workers can inhale infectious airborne particles while treating a coughing patient. Face shields can substantially reduce the short-term exposure of health care workers to large infectious aerosol particles, but smaller particles can remain airborne longer and flow around the face shield more easily to be inhaled. Thus, face shields provide a useful adjunct to respiratory protection for workers caring for patients with respiratory infections. However, they cannot be used as a substitute for respiratory protection when it is needed.

Face shields for infection control: A review

“…[12] However, as highlighted in a recent Institute of Medicine report, [15] little is known about the effectiveness of face shields in preventing the transmission of viral respiratory diseases. Utilizing a cough aerosol simulator loaded with influenza virus (aerosol volume mean diameter of 8.5 µm) and a breathing simulator, Lindsley et al [16] reported 96% and 92% reductions in the risk of inhalational exposure immediately after a cough for a face shield at distances of 18 in (46 cm) and 72 in (183 cm), respectively. Decreasing the aerosol size to 3.4 µm resulted in the face shield blocking 68% of the inhalational exposure at 18 in (46 cm) immediately after the cough and 23% over 1-30 min post-cough (during which time the larger aerosol particles had settled out and droplet nuclei had formed and remained airborne so that flow occurred more easily around the edges of the face shield).…”

“…Decreasing the aerosol size to 3.4 µm resulted in the face shield blocking 68% of the inhalational exposure at 18 in (46 cm) immediately after the cough and 23% over 1-30 min post-cough (during which time the larger aerosol particles had settled out and droplet nuclei had formed and remained airborne so that flow occurred more easily around the edges of the face shield). [16] Shoham et al [17] sprayed a fluorescent dye (particle diameter ∼5µm) at a distance of 20 in (50 cm) away from a mannequin head outfitted with various types of PPE. They found that a face shield with head/neck length, three separate contact points at the forehead, and side curve reaching to the point of the ear (Bettershield TM , Southmedic, Barrie, Ontario, CA), or the combination of this face shield and an N95 filtering facepiece respirator (N95 FFR), protected the eyes, nares and mouth from contamination.…”

“…[12] Use of a face shield alone for eye, face, and mucous membrane protection from contamination by body fluids is likely insufficient and it has been recommended that in those situations where a face shield is used to protect against splash or splatter, a medical/surgical mask would also be indicated. [33] Face shields are not meant to function as primary respiratory protection and should not be used alone because aerosols can flow behind the visor, [16,19,21,41] so a protective facemask (medical/surgical mask, N95 FFR, etc.) should be worn concurrently.…”

Annual Burden of Occupationally‐Acquired Influenza Infections in Hospitals and Emergency Departments in the United States

“…Hand hygiene Fraction of virus remaining on hands after hand hygiene 0.05 (18,19) 40% (16,(20)(21)(22) Eye protection Fraction of virus that bypasses the goggles or face shield 0.04 (23) 50% Facemask Fraction of sprayed and contact-transferred virus that penetrates or bypasses facemask 0.10 b (24,25) 50% b (16,17,(25)(26)(27) Percent reduction in frequency of contact with the facial portals 90% (28) N95 filtering facepiece respirator Fraction of sprayed and contact-transferred virus that penetrates through respirator 0.05 b 20% b (16,17,(25)(26)(27) Protection factor d Uniform: range 5-10 (29,30) Percent reduction in frequency of contact with the facial portals 90% (28) Isolation Fraction reduction in the duration of occupational exposure 0.18 (7) 80% (31)(32)(33)(34) Percent increase in compliance with hand hygiene, eye protection, facemasks or respirators, and full compliance with gloves 25% (7,32,35,36) Surface decontamination Fraction of virus remaining on surfaces 0.05 (37,38) 50% e The protection factor is a ratio of the concentration of particles outside the respirator to that inside. The assigned protection factor of these respirators is 10 (30) , but lower performance was considered due to issues with long-term fit and use practices.…”

U.S. Medical Examiner/Coroner capability to handle highly infectious decedents

“…N95 respirator or PAPR) [33,38,39]. Use of a face shield rather than glasses/goggles also has been shown to reduce contamination of respirators by particles but only 59% of ME/C respondents routinely wear them [40].…”