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Tuesday, May 12, 2020

How Coronavirus Spreads through the Air: What We Know So Far

How Coronavirus Spreads About 100 years ago we suspected that infection may spread when coughing and sneezing. Petri dishes were placed in rooms of persons coughing and sneezing in order to isolate potential pathogens. This was the origin of “droplets“ as a means of infection transmission. Literally, particles large enough to drop out of the air into bowls called Petri dishes. But, this was an insufficient explanation for all cases. We noticed that sometimes people got sick with the same illness when they were not in close proximity with the little person at the same time. So, we considered the prospect of “airborne“ transmission. This was evaluated in the early days of tuberculosis by placing guinea pigs into the air ducts of tuberculosis sanitariums. The guinea pigs were not in the same room as the patient, thus, were not exposed to the heavy droplets; but, they did share the same airflow from those rooms. Many of the guinea pigs came down with tuberculosis infection; thus, the concept of airborne transmission was solidified. Since those early days, we have sought to characterize respiratory infection transmissions as EITHER droplets or airborne. However, a cough and a sneeze is an aerosol which is a combination of BOTH droplets and aerosols. This complicated matters. Overall, although both droplet and airborne mechanisms may be at hand, we tend to designate the mechanism according to the major clinical pattern of transmission.
from Rajesh Harrykissoon, MD

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