six feet?

It always used to be ten, that being the length of the pole with which you wouldn’t want to touch the ugly girl in school.  But ever since the CDC started making announcements in February about what we need to do to protect ourselves from COVID-19, it’s been six feet we’re to be kept apart, 2 good arm’s lengths of a pretty tall person.  WHO, lording over the rest of the world, mandates only 3 feet of separation (a meter, 39.37 inches, actually).  But where are they getting this stuff?  Well, it turns out they’re not totally making this up.

The obvious notion that respiratory illness is spread by droplets containing the bug emitted by the infected person dates to an 1897 report by Carl Flügge, a German bacteriologist and hygienist.  Engineer William Wells of Harvard reported in 1934 on the travel of droplets containing the most important respiratory pathogen of that day, tuberculosis. He used a very simple calculation to conclude that large droplets travelled about 3 feet but no more than 6 feet before falling to the ground.  He also discovered that small droplets were too light to succumb to gravity so could travel even further.  This informed the WHO’s guidelines.  The CDC leaned on more recent research, conducted after the 2003 SARS outbreak (COVID-19’s full name is “SARS-CoV-2”; it’s a very closely related coronavirus).  16 investigators coordinated by the CDC, but flung as far as Singapore, Taiwan, China and Thailand, looked at passengers who had acquired SARS on 3 long distance flights carrying known infected patients (https://www.nejm.org/doi/full/10.1056/nejmoa031349).  One flight carrying 315 passengers from Hong Kong to Taipei contained one passenger who only got sick later and did not infect anyone else.  In a flight from Hong Kong to Beijing, surprise, it was riskier to sit close to a SARS patient, with 8 of the 23 passengers who were seated in the same row as the patient or in the three rows in front of him becoming infected, as compared with 10 of the 88 passengers who were seated elsewhere (relative risk, 3.1; 95 percent confidence interval, 1.4 to 6.9). 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.  Of course, there’s no better place to promulgate an airborne infection than the cabin of an airplane with its pressurized non-circulated air. In a flight that followed from Hong Kong to Taipei, 4 of the infected passengers from the previous flight were among the 246 aboard.  Of 166 later interviewed, only one got sick (fever and cough) but tested negative for SARS. But there’s your 6 foot rule.

Dr. Bourouiba of The Fluid Dynamics of Disease Transmission Laboratory at MIT found that a good cough or sneeze can propel droplets as far as 23-27 feet (https://jamanetwork.com/journals/jama/fullarticle/2763852).  Yikes!  And that cloud can stay airborne for quite a while, even wending its way through air circulation systems.  More reason to get outdoors as much as possible.

Just last month, 6 authors on behalf of the COVID-19 Systematic Urgent Review Group Effort (SURGE) published in Lancet (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext) “Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and metanalysis”.  They identified 172 observational studies across 16 countries and six continents. Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m; protection was increased as distance was lengthened.  Face mask use could result in a large reduction in risk of infection, with stronger associations with N95 or similar respirators compared with disposable surgical masks. Eye protection also was associated with less infection.

So, yep, getting farther away and putting up barriers seems to help protect.  But only this guy is really safe:

Sad state.  Me, I’m for as many to get infected as soon as possible to build up that herd immunity.  In the meantime, let me propose a couple of theme songs for this issue:

It’s a cliché by now, but stay safe.