How Far Can a Sneeze Go?

Posted on by Jesse Santiano, M.D.

The current CDC recommendation for social distancing is 6 feet or 2 meters. The thought is that at 6 feet, the droplets from coughing or sneezing would land on a surface and prevent the spread of Covid-19.

The 6-feet length may have come from a study about the Severe Acute Respiratory Syndrome or SARS epidemic in 2003. In that epidemic, SARS transmission was studied in a Boeing 737-300 flight from Hong Kong to Beijing, where one person infected 18 others.

That study was published in the New England Journal of Medicine. From the study, we learn that passengers from 3 economy seats away were infected by one SARS patient. The distance to the ones who later got SARS was 2.3 meters or 7.5 feet.

Fast forward to today, a clinical review by Dr. Lydia Bourouiba from The Fluid Dynamics of Disease Transmission Laboratory, Massachusetts Institute of Technology, was published in the Journal of the American Medical Association.  The review sheds new knowledge about the distance and spread of the droplets produced by sneezing and coughing.

The letter was based on previous studies by the same author. They found out that coughing and sneezing produce a dust cloud with large and small droplets.  Being inside a warm and humid gas cloud, the droplets in it take longer to evaporate than if they are alone. Because of the gas cloud, the life of a droplet gets longer. From a split second to minutes.

They also found that those virus-laden droplets can travel to as far as 23 to 27 feet or 7-8 meters. Here is a link from JAMA that shows a video of a sneeze and the resulting gas cloud.

The droplets will settle on any surface within that distance, depending on their size. Those surfaces become contagious. The droplets can also be inhaled by someone socially distancing themselves at 6 feet.

Some of the droplets can evaporate while in the air. More so if the air is dry and warm. Dry air is present during the heating time in winter and also in air-conditioned places. One way that an air-conditioner cools the air is by removing humidity. Once dried, the virus particles become aerosols.

1280px-Sneeze

Infectious aerosolized viral particles have been demonstrated to stay suspended in the air for at least 16 hours, as shown by a study from Tulane University.

Regular talk by an asymptomatic carrier can also transmit viruses, as shown in this article.

What should we do then? Should people increase their social distance to 27 feet or 8 meters? I think the answer depends on everyone’s situation. For example, if someone is known to be positive for Covid-19 and actively coughing or sneezing, then masks should be worn by all parties if it is not possible to avoid that person.

Mask wearing, hand washing, and disinfecting still apply to all.

Image Credit: Sneezing by James Gathany – CDC Public Health Image library ID 11162

Related:

  1. Covid-19 Spread with Air-conditioning

  2. Study Explains the Silent Spread of Covid-19

  3. Will the Pandemic get Better with Warm Weather?

  4. The Asymptomatic and Symptomatic Covid-19 are Equally Infectious

  5. Can Talking Spread Viruses?

  6. 5 Reasons why Covid-19 Spreads Fast

  7. SARS-CoV-2 Contamination in the Hospital Setting

  8. How Long Can the Covid-19 Virus Survive in Common Surfaces?

  9. SARS-CoV-2 Contamination in the Hospital Setting

  10. How Long does the Covid-19 Virus Float in the Air and Stay on Surface?

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