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Science Magazine Perspective: Reducing Transmission of SARS-COV-2 (and my thoughts on a Republican convention without masks)

2020-06-01

photo by Juraj Varga courtesy of pixabay.com

From the article, published May 27 (bolding added for emphasis):

Respiratory infections occur through the transmission of virus-containing droplets (>5 to 10 μm) and aerosols (≤5 μm) exhaled from infected individuals during breathing, speaking, coughing, and sneezing. Traditional respiratory disease control measures are designed to reduce transmission by droplets produced in the sneezes and coughs of infected individuals. However, a large proportion of the spread of coronavirus disease 2019 (COVID-19) appears to be occurring through airborne transmission of aerosols produced by asymptomatic individuals during breathing and speaking (13). Aerosols can accumulate, remain infectious in indoor air for hours, and be easily inhaled deep into the lungs. For society to resume, measures designed to reduce aerosol transmission must be implemented, including universal masking and regular, widespread testing to identify and isolate infected asymptomatic individuals.

Identifying infected individuals to curb SARS-CoV-2 transmission is more challenging compared to SARS and other respiratory viruses because infected individuals can be highly contagious for several days, peaking on or before symptoms occur (27). These “silent shedders” could be critical drivers of the enhanced spread of SARS-CoV-2. In Wuhan, China, it has been estimated that undiagnosed cases of COVID-19 infection, who were presumably asymptomatic, were responsible for up to 79% of viral infections (3). Therefore, regular, widespread testing is essential to identify and isolate infected asymptomatic individuals.

The World Health Organization (WHO) recommendations for social distancing of 6 ft and hand washing to reduce the spread of SARS-CoV-2 are based on studies of respiratory droplets carried out in the 1930s. These studies showed that large, ~100 μm droplets produced in coughs and sneezes quickly underwent gravitational settling (1). However, when these studies were conducted, the technology did not exist for detecting submicron aerosols. As a comparison, calculations predict that in still air, a 100-μm droplet will settle to the ground from 8 ft in 4.6 s whereas a 1-μm aerosol particle will take 12.4 hours (4). Measurements now show that intense coughs and sneezes that propel larger droplets more than 20 ft can also create thousands of aerosols that can travel even further (1). Increasing evidence for SARS-CoV-2 suggests the 6 ft WHO recommendation is likely not enough under many indoor conditions where aerosols can remain airborne for hours, accumulate over time, and follow air flows over distances further than 6 ft (510).

Airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing, and social distancing programs. After evidence revealed that airborne transmission by asymptomatic individuals might be a key driver in the global spread of COVID-19, the WHO recommended universal use of face masks. Masks provide a critical barrier, reducing the number of infectious viruses in exhaled breath, especially of asymptomatic people and those with mild symptoms (12) (see the figure). Surgical mask material reduces the likelihood and severity of COVID-19 by substantially reducing airborne viral concentrations (13). Masks also protect uninfected individuals from SARS-CoV-2 aerosols (1213). Thus, it is particularly important to wear masks in locations with conditions that can accumulate high concentrations of viruses, such as health care settings, airplanes, restaurants, and other crowded places with reduced ventilation. The aerosol filtering efficiency of different materials, thicknesses, and layers used in properly fitted homemade masks was recently found to be similar to that of the medical masks that were tested (14). Thus, the option of universal masking is no longer held back by shortages.

To illustrate the perniciousness of ignorance, a recent news story claimed that, in a telephone conversation between the governor of the State of North Carolina and the president regarding the possibility of holding a Republican National nominating convention in that state, the president demanded that the convention be held with a full hall and that no masks be worn by attendees.  This situation would present the most infectious possible setting for a national meeting, yet it is what the president demands in order to whip up the enthusiasm of his base.  What would happen if his demands were accepted?  A few asymptomatic people could have infected the entire hall, possibly resulting in spread of cases nationwide after the attendees returned home.  Such a “superspreader” event would be a tragedy for Republicans nationally but a “victory” for the president.  What price ignorance and narcissism?

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