A recent study published in JAMA created a lot of interest as it reported that when a person coughs or sneezes, small droplets may travel up to 7-8 meters. The study stated that coughs and sneezes are primarily made of a turbulent gas cloud that traps the droplets. Because of the moist and warm atmosphere within the turbulent gas cloud, small droplets may not evaporate as quickly as they are supposed to. This results in the propulsion of these tiny droplets up to 7-8 meters or 23 to 27 feet. Finally, the study raised concerns that there may be a risk of coronavirus droplets traveling up to 7-8 meters. The study also questioned if the social distancing norms – 1 meter recommended by World Health Organization (WHO) and 2 meters recommended by Centers for Disease Control and Prevention (CDC), are sufficient to prevent transmission of COVID-19 in the community.
It is valid that the tiny droplets in coughs and sneezes travel much longer, up to 6-8 meters. In fact, this is not the first study to report that tiny droplets travel such a long distance. The same author of the above research also published in the NEJM journal in 2016, an image of droplets traveling a long distance. Similarly, in the journal Indoor Air, a study was published in 2007, demonstrating that tiny droplets in coughs and sneezes can travel up to 6-8 meters. Also, according to a study published in JAMA, in March 2020, Novel Coronavirus particles could be found in the ventilation systems in the hospital rooms where COVID-19 patients were staying.
However, none of the above studies demonstrated the ability of these virus particles to infect (infectivity) at a distance of 6-8 meters from the patients. Based on the available research, it is a well known fact that the viral load in the droplets diminishes as the distance from the patient gets longer and longer. According to a study published by Morawska et al., infectivity of the tiny droplets or the hazard created depends on several factors including: (1) the type of virus and potential health effects it causes; (2) mode of exit from the body; (3) concentration levels, (4) size distribution of aerosol containing the virus; (5) physical characteristics of the environment (temperature, humidity, oxygenation, UV light, suspension medium, etc.); (6) air circulation pattern; and (7) operation of heating, ventilation and air-conditioning system.
One study published in the Journal of Infectious Diseases, infectious amounts of influenza virus was detected up to 6 feet from the patients. Beyond 6 feet, droplets do not have enough viral load to be infectious. Similarly, other studies detected influenza virus in the air in close proximity to the patient. So far, there are no studies that detected influenza or other respiratory viruses in an infectious amount beyond six feet from the affected person. During certain medical procedures like bronchoscopy, intubation, nebulizations, BIPAP treatment, aerosols may be produced, and they may infect healthy individuals at a longer distance. This airborne transmission is rare in a community setting.
In summary, coughs and sneezes can expel small droplets to a distance of 6-8 meters. As droplets travel farther, infectious amount of viruses in these droplets is significantly reduced. So far, there is no evidence to prove that these droplets can infect a healthy person beyond six feet from the infected person.
Bourouiba L. Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19. JAMA. Published online March 26, 2020. doi:10.1001/jama.2020.4756
Bourouiba L. IMAGES IN CLINICAL MEDICINE. A Sneeze. N Engl J Med. 2016 Aug 25;375(8):e15. doi: 10.1056/NEJMicm1501197.
Xie X et al. How far droplets can move in indoor environments--revisiting the Wells evaporation-falling curve. Indoor Air. 2007 Jun;17(3):211-25.
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