Slide 1: 6 feet apart. A restaurant in Maryland is promoting social distancing by having their patrons wear a 3 foot inner tube to ensure all guests maintain at least 6 feet from each other. While this may be a fun, clever way to enforce social distancing, where does the 6 foot social distancing recommendation come from?
Slide 2: The answer isn’t straightforward. Much of the data for the “6 foot (2 meter) rule” originated before the 1950s! These studies had individuals with bacterial infections (beta hemolytic streptococci) sit in rooms with agar plates at fixed distances on the floor. Individuals were asked to cough and sneeze. Researchers determined the farthest distance from the patient that bacteria could still be isolated from the agar plate.
Slide 3: While these models based on bacterial infections showed that most infectious droplets fell short of 6 feet, up to 10% of patients could still generate aerosols that travelled as far as 9.5 feet (2.9 meters).
Slide 4: To make things even murkier, modern day epidemiological studies show that a myriad of variables influence how far infectious particles can spread. It’s ultimately impossible to define a universally applicable physical distancing rule.
Indoors. Air flow patterns, air handling systems, and ventilation all influence how long infectious particle remain in the air. It’s generally shown that being indoors is a higher infection risk than being outdoors.
Activities. Activities such as singing, talking loudly, and indoor exercise all increase aerosol production through violent exhalation.
Physical barriers. Barriers such as masks or partitions limit the capability for droplets to spread.
Environment & Infectious Agents. A complex interplay between intrinsic variables of infectious particles (size, hydrophilic nature) and environmental factors (air temperature, humidity) influence the likelihood that infection can be transmitted via airborne transmission.
So if we can’t rely on inner tubes to keep us safe, what can we do to prevent spread of COVID-19? We can limit group activities that generate aerosols (i.e. singing, shouting, exercise), avoid others if symptomatic, avoid spending prolonged time with others in small, poorly ventilated indoor settings, and wear face coverings.
- Lee E. ‘Bumper tables’ made of inner tubes: Here’s how one Ocean City restaurant plans to enforce social distancing. The Baltimore Sun. 2020 May 18. Link.
- Hamburger M Jr, Robertson OH. Expulsion of group A hemolytic streptococci in droplets and droplet nuclei by sneezing, coughing and talking. Am J Med. 1948 May;4(5):690-701. PMID 18856764.
- Jones NR, Qureshi ZU, Temple RJ, Larwood JPJ, Greenhalgh T, Bourouiba L. Two metres or one: what is the evidence for physical distancing in covid-19? BMJ. 2020 Aug 25;370:m3223. PMID 32843355.
Tags: 6 foot rule, corona virus, COVID-19, immunology, public health