Virus Droplets Could Travel 27 Feet, Social Distancing Rules Outdated: MIT Professor

Scanning electron microscope image shows the CCP virus (round blue objects) emerging from the surface of cells cultured in the lab. NIAID-RML

Droplets from the CCP virus could travel up to 27 feet, a Massachusetts Institute of Technology (MIT) researcher stated in a paper published in the Journal of the American Medical Association on March 26.

Lydia Bourouiba, an associate professor at MIT and expert in fluid dynamics, said a sneeze or cough, for example, results in a turbulent gas cloud that could contain virus droplets, and warned that the current guidelines on social distancing, while critical in the current time of pandemic, are based on outdated models from the 1930s.

“Recent 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,” she wrote.

“Owing to the forward momentum of the cloud, pathogen-bearing droplets are propelled much farther than if they were emitted in isolation without a turbulent puff cloud trapping and carrying them forward,” Bourouiba wrote. “Given various combinations of an individual patient’s physiology and environmental conditions, such as humidity and temperature, the gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet (7–8 meters).”

Bourouiba also noted that peak exhalation speeds can reach 33 to 100 feet per second, thus creating a cloud that can span approximately 23 to 27 feet, and that “currently used surgical and N95 masks are not tested for these potential characteristics of respiratory emissions,” adding that “turbulent gas cloud dynamics should influence the design and recommended use of surgical and other masks.”

Speaking to USA Today, Bourouiba said there is an “urgency in revising the guidelines currently being given by the [World Health Organization] and the [Centers for Disease Control and Prevention] on the needs for protective equipment, particularly for the frontline health care workers.”

The professor’s research is at odds with the advice issued by the Centers for Disease Control and Prevention to maintain social distancing of at least six feet to limit the risk of exposure, while the World Health Organization advises three feet of space between people. President Donald Trump this week also announced he will extend his administration’s “15 days to slow the spread” campaign, which maintains the same social distancing guidelines, through April 30.

The White House guidelines also call on Americans to avoid social gatherings in groups of more than 10 people, refrain from eating in bars, restaurants, and food courts, avoid non-essential travel, and to not visit nursing homes. They also include basic sanitary measures such as washing hands frequently and not touching one’s face.

Following the publication of Bourouiba’s MIT study, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, urged the public to be cautious, noting that the research “could really be terribly misleading.”

Speaking at a White House briefing on March 31, Fauci said, “What it was, was looking at the distance droplets fly by speaking, coughing, and sneezing,” adding that it would only apply to people with extremely strong, “vigorous and robust” sneezes. “I was disturbed by that report because that’s misleading; that means that all of a sudden, the six-foot thing doesn’t work.”