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Social Distancing – 6 Feet or 3 Feet? Depends If You Follow the CDC or the WHO

hat CaptureIn U.S. we have been told to keep a 6 foot social distancing barrier between anyone we come in contact with. This recommendation comes from the Centers for Disease Control and Prevention (CDC), while the World Health Organization (WHO) recommends at least one metre (3.2 feet).

In France which follows the WHO recommendation, a Chinese woman living in Paris, interviewed by La Parisien, created a social distancing hat to wear in the street with straight flaps on each side to stop people getting too close.

The sign says, “ceci est un chapeau d’un mètre, veuillez respecter la distance” (this is a one-metre hat, please respect the distance). She reported she had been inspired by a traditional hat from the Song dynasty, which used to be worn by the subjects of the emperor to avoid them getting too close and plotting against him. She told Le Parisien: “I wanted to something fun to make people laugh and show them what is the distance of one metre.”

The WHO’s three-foot recommendation originates with work done in the 1930s by Harvard researcher, William Wells, who studied tuberculosis. He found that droplets – bits of spit, mucus, and phlegm emitted when we breathe, cough, or sneeze – tend to land within three feet of where they’re expelled. His findings were reported in the American Journal of Epidemiology, in 1934

The CDC may have adopted the 6 foot rule after a 2003 study of SARS on three planes, published in the New England Journal of Medicine. After one flight carrying a symptomatic person and 119 other persons, laboratory-confirmed SARS developed in 16 persons, 2 others were given diagnoses of probable SARS.

“The risk of illness was related to the proximity to the index patient, with illness reported in 8 of the 23 passengers who were seated in the same row as the patient or in the three rows in front of him, as compared with 10 of the 88 passengers who were seated elsewhere. It is notable that 56 percent of the passengers who became infected were not seated in the same row as the index patient or in the three rows in front of him.”

On one of the planes, “90 percent of the persons who became ill were seated more than 36 in. away from the index patient.”

NOTE – “Aircraft ventilation systems are believed to be highly efficient at keeping the air free of pathogens, which they do by exchanging the air in passenger cabins every three to four minutes and passing the circulated air through high-efficiency particulate-arresting (HEPA) filters designed to filter out all particles larger than 0.3 μm by 1 μm.”

Quartz reported they tried to find the origins of the six-foot guideline with the CDC, but after multiple attempts over two weeks, the agency failed to comment.

A 2013 study in The Journal of Infectious Diseases, “established that HCPs (Healthcare professionals) could be exposed to airborne influenza virus at a distance of up to 1.829 m (6 feet) from a patient with symptomatic influenza virus infection.”

Depending what country you live in determines what social distancing rule you have to follow. The UK, Switzerland, Spain, Italy, and Republic of Ireland have set a 6 metre rule. Austria, Finland, Sweden, Denmark and Norway have a 1 metre rule, while in Germany, Poland, and the Netherlands it’s 1.5 metres (4.9 feet).

Professor Robert Dingwall, a sociologist at Nottingham Trent University and a member of government advisory group NERVTAG (New and Emerging Respiratory Virus Threats Advisory Group), has criticized the UK 2 metre rule.

“The World Health Organization recommends a one metre distance, If you probe around the recommendations of distance in Europe you will find that a lot of countries have also gone for this really on the basis of a better understanding of the scientific evidence around the possible transmission of infection.”

He reported that officials had told him they “did not think the British population would understand what one metre was and we could not trust them to observe it so we doubled it to be on the safe side. The two-metre rule was conjured up out of nowhere.”

Danish Health Authority announced people only need to keep 1 metre from each other in public areas. “We are here clarifying that in most cases, a minimum of 1 metre is sufficient,” the authority said in a press release.

The early release of information from a research project that used computational fluid dynamics software suggested that walkers should stay at least 13 feet away, fast runners around 30 feet, and cyclists up to 65 feet depending on their speed. The news was reported in the Medium and went viral and sent out shockwaves.

The problem, Outside magazine noted, was that the study had limitations. “In general, the risk of transmission outdoors is much lower unless you’re in a crowded location,” says Linsey Marr, a professor of civil and environmental engineering at Virginia Tech. “In practice, you need to be in the presence of a high concentration of virions to be at high risk.”

And then there’s research by Dr Lydia Bourouiba at MIT who studies the dynamics of exhalations (coughs and sneezes). She suggested exhalations cause gaseous clouds that can travel up to 27 feet. 

That’s questionable says Professor Dr  Paul Pottinger, an infectious disease expert at the University of Washington School of Medicine. If it was true more people would be sick and more could have been affected.

“For me, the question is not how far the germs can travel, but how far can they travel before they’re no longer a threat. The smaller the germ particles, the lower the risk that they might infect somebody who would breathe them in or get them stuck in their nose or their mouth.”

 

 

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