Overview of Method of Transmission/PPE
The World Health Organization recognizes COVID-19 as a droplet-borne
disease unless an aerosol-generating procedure is performed (e.g.
non-invasive positive pressure ventilation, bronchoscopy, open
suctioning, endotracheal intubation, cardiopulmonary resuscitation,
tracheostomy, and administration of nebulized treatment). Currently,
coughing and sneezing are categorized as droplet-producing, not
aerosolizing, by both the Centers for Disease Control (CDC) and World
Health Organization (WHO). Droplet transmission occurs via respiratory
droplets between 5-10 micrometers when an at-risk individual is within 1
meter of the source. Airborne transmission occurs in so-called droplet
“nuclei” measuring fewer than 5 micrometers capable of traveling for
distances greater than 1 meter, such as the case during AGPs. While
several publications have reported SARS-CoV2 aerosolization risk with
coughing or sneezing, although, so far, the WHO has maintained that
additional research is necessary to verify these claims, citing issues
either with using RNA detection as a proxy for the presence of viable
virus, or the method by which inoculum was aerosolized.4–6
Loose-fitting, standard surgical facemasks, together with a face-shield
or eye protection, are considered protective against droplets.
Fit-tested N95 filtering facepiece respirators, along with tight-fitting
eye protection or face-shields with side protection to shield the
conjunctiva are indicated for providers when there is a risk for
airborne transmission. Powered air-purifying respirators (PAPR)
represent a reusable alternative to N95s for protection against airborne
transmission. Although there is a quantitative difference in the
filtering efficacy of N95 filtration masks (assigned protection factor
[APF] of 10, indicating that 90% of airborne particles are blocked
from inhalation) versus PAPR (APF of up to 1000 for a full facepiece
PAPR), neither the CDC nor the WHO have clearly characterized a
clinically-discernible difference with standard use. 7While the N95 requires mask-fit testing, PAPR requires training to guide
proper assembly and troubleshooting of components (e.g. battery, hose,
filter, etc.), donning and doffing, and may pose unique visibility
issues (e.g. fogging, inability to use headlight) in the operating room.
Moreover, headaches are common amongst healthcare workers wearing N95
masks 8, a phenomenon postulated to be related to
impaired gas exchange with retention of carbon dioxide, or mechanical
factors associated with prolonged N95 mask usage. 9