How COVID-19 Spreads. Do Faces Masks Help?
Infectious diseases like COVID-19 are spread by close contact with its droplets.
Arosolization is the pathway of spreading infection. Coughing and sneezing are the most obvious forms of transmission.
According to the National Academy of Sciences (NAS), talking and breathing out can also spread the virus from an infected person to others.
Dr. Harvey Fineberg heads NAS’ Standing Committee on Emerging Infectious Diseases and 21th Century Health Threats.
By letter to White House office of science and technology policy director Kelvin Droegemeier, he said the following:
“(R)esults of available studies are consistent with arosolization of the virus from normal breathing” and talking.
Coughing and sneezing can emit large respiratory droplets, exhaling and talking minute ones.
They aerosolize and deposit droplets on surfaces, including face masks and other personal protective gear (PPE) — why medical staff need to change PPE frequently, a new face mask per patient.
Indoors they can remain aerosolized for a considerable time after being emitted.
Outdoors they disperse much more quickly. Healthy individuals can be infected by transferring contaminants from hands to their mouth, nose, or eyes.
A New England Journal of Medicine report explained that COVID-19 aerosol droplets less than 5 microns in size can remain aerosolized indoors for up to 3 hours and stay infectious.
According to Fineberg, when medical staff remove face masks and other PPE, COVID-19 droplets can remain in the air for hours and infect others in the area.
A study by Dr. Nancy Leung and colleagues concluded the following:
“Our results provide mechanistic evidence that surgical face masks could prevent transmission of human coronavirus and influenza virus infections if worn by symptomatic individuals.”
Most face masks provide little protection for healthy individuals. Because a significant number of COVID-19 infected individuals are asymptomatic, it makes sense to wear one in public to prevent against greater spread of the virus unwittingly to others by carriers.
According to the National Institute for Occupational Safety and Health (NIOSH), N95 respirator masks protect against a minimum of 95% of airborne particles because they provide a tight seal around the mouth and nose.
Ordinary face masks do not because they’re loose-fitting. They’re most effective in preventing the risk of droplets from infected people spreading to others.
At the present time in the US, N95s are in short supply, hard to get for medical staff, near-impossible for most people.
This week I spoke to an importer and distributor of N95s. The firm’s head told me he has none in stock and doesn’t expect a new supply for about a month or longer.
On its website, Amazon said it prioritizes sales of N95s to hospitals and government agencies as supplies become available, adding:
“Inventory is currently very limited.” At this time, sales to the public were halted.
A number of N95 sellers I checked with had none available for sale to the public.
Demand way exceeds supply, a situation not likely to change any time soon, perhaps not until they’re no longer needed.
It’s unclear how many of these masks were hoarded to sell at highly inflated prices in the black or gray market.
They’re produced in the US and abroad, notably in China.
MIT Professor Lydia Bourouiba has expertise in fundamental fluid dynamics, instabilities, interfacial flows, pathogen-fluid interactions, contamination, contact and disease transmission, infectious diseases, infection control, and epidemiology.
She explained that “(r)ecent work has demonstrated that exhalations, sneezes, and coughs not only consist of mucosalivary droplets following short-range semiballistic emission trajectories but, importantly, are primarily made of a multiphase turbulent gas (a puff) cloud that entrains ambient air and traps and carries within it clusters of droplets with a continuum of droplet sizes,” adding:
“Droplets that settle along the trajectory can contaminate surfaces, while the rest remain trapped and clustered in the moving cloud.”
“Eventually the cloud and its droplet payload lose momentum and coherence, and the remaining droplets within the cloud evaporate, producing residues or droplet nuclei that may stay suspended in the air for hours, following airflow patterns imposed by ventilation or climate-control systems.”
Social distancing guidelines call for staying 6 feet away from others — based on outdated models from the 1930s.
Bourouiba said COVID-19 droplets can travel up to 27 feet and linger for hours indoors, adding:
“(V)irus particles could be found in the ventilation systems in hospital rooms of patients with COVID-19,” a worrisome finding because it risks spreading contamination from one room to others and hallways.
If a hospital has many COVID-19 patients, Bourouiba’s findings suggest the risk that much of the facility could become contaminated with COVID-19 droplets.
She called White House guidelines “overly simplified.” They “may limit the effectiveness of the proposed interventions” against COVID-19.
Medical staff face an “under-appreciated potential exposure range” in treating COVID-19 patients.
“There’s an urgency in revising the guidelines currently being given by the (WHO) and (CDC) on the needs for protective equipment, particularly for the frontline health care workers.”
On March 26, Bourouiba’s detailed analysis was published by the Journal of the American Medical Association (JAMA), titled:
“Turbulent Gas Clouds and Respiratory Pathogen Emissions
Potential Implications for Reducing Transmission of COVID-19”
The article provides detailed information on the issue, some technical, but laymen can understand her underlying message on a crucial issue our time.
My newest book as editor and contributor is titled “Flashpoint in Ukraine: How the US Drive for Hegemony Risks WW III.”