The CDC has recommended that Americans wear masks “in public”, but are vague on what to do if you are alone and unlikely to come in close contact with others while you’re outside.
From the CDC website: “CDC recommends that people wear masks in public settings and when around people who don’t live in your household, especially when other social distancing measures are difficult to maintain.”
The question few people ask is: what qualifies as “in public”? You’re out in public if your walking in New York’s Times Square, but you’re also out in public is you’re hiking alone in the Smoky Mountains National Park. There are a lot of times, depending on where you live, that a walk around the block is unlikely to encounter a neighbor outside their house.
The answer you’ll be given is to practice “Safe Six”. Six feet (two meters) of distance from other people is thought to be the safe distance between yourself and another person. Social distancing and the wearing of masks in crowds during epidemic outbreaks is something I’ve written about since the 2009 Swine Flu pandemic. Now, it’s national policy.
Are current thoughts on social distancing based on hard data? How did the medical establishment decide that six feet was the benchmark for acceptable social distancing? A cough or sneeze can project viral particles more than twenty feet in some circumstances. A number of different activities that provide air flow, like coughing, sneezing, singing, shouting, and even simple exhalation can extend the range of droplet spread.
A recent study published in the prestigious British Medical Journal considers “Safe Six” an oversimplification of what the risks really are. Your risk of contagion depends on many factors. Are you indoors or outdoors? in crowded spaces or alone? These considerations and others determine your real risk of contracting the SARS-CoV2 virus.
In some high-risk settings, it seems reasonable that recommendations should be stricter and provide more protection. In low-risk situations, there should be more freedom, possibly allowing a return to a more normal life for most.
The British Medical Journal study is worth reading in its entirety:
Distancing from sick individuals, for better or worse, has a long history. In ancient times, people stayed away from “leper” colonies (leprosy is now known as “Hansen’s Disease”). People would avoid visiting cities undergoing outbreaks of the plague. No one really knew, however, how much distance was required.
An experiment performed in 1897 first suggested 1-2 meters (3-6 feet) as the benchmark for infectivity due to airborne droplet spread. At the time, visible droplets for coughs and sneezes were collected and found to contain streptococcal bacteria at those distances. When these droplets landed in the mouths or noses of people nearby, they often got sick.
Decades later, advances in microscopy allowed better visualization. A 1948 study identified that 65% of subjects produced large droplets but fewer than 10% traveled as far as 5 ½ feet. In those whose droplets traveled at least that far, however, pathogens were recovered 9-10 feet away. Other studies report that large droplets fall through the air quickly, landing on surfaces rather than circulating around.
At present, A United Kingdom advisory group estimates he risk of SARS-CoV2 transmission to be 2-10 times higher at 1 meter than 2 meters. The World Health Organization suggests that the risk of transmitting COVID-19 is about 12.8% at distances less than 3 feet and 2.6% if greater.
SMALL AIRBORNE DROPLETS
Droplets are not all large. They exist across an entire spectrum of sizes. Small droplets, also called aerosol droplets, mostly evaporate close to the exhaled source before they fall. Without airflow, they don’t travel far. If there is an air current, however, they can travel further than large droplets. This is especially an issue with indoor ventilation, where the viral concentration is higher.
Seven out of nine hospital studies revealed positive presence of SARS-CoV2 RNA in air samples (positive rate varied widely from 2 -64 percent). The presence of viral particles in the air doesn’t necessary mean they can replicate. Only two of the nine studies determined whether the viral droplet particles retained that ability. One did, one didn’t. None of the studies, by the way, found viable virus on swabs taken from surfaces.
These results are both good news and bad news. In certain circumstances, droplet spread may not travel as far as previously thought and may remain viable for less time on surfaces. On the other hand, simply singing in the church choir increases the risk of transmission.
Some results came out as you might expect: A number of people vigorously exercising in an indoor gym exhale forcefully, increasing the risk of droplet spread. The same people have much less chance of passing virus onto others if activities are held outside and avoid groups, where respiratory droplets are quickly diluted. A yet unpublished study suggests a risk of transmission almost nineteen times greater indoors than out.
At this time, being outside is generally considered safer than being inside. When taking a stroll or participating in other outdoor activities by yourself or with people you live with, a mask isn’t required.
However, when you find it difficult to maintain at least six feet of distance from people you don’t live with – such as at a restaurant or passing someone on a sidewalk. it’s important to have your mask on. You should always have your mask on hand when you leave your home.
(Aside: How long does a person have to be exposed to COVID-19 patients to increase the risk of transmission? Contact tracing suggests about five to fifteen minutes, but the data isn’t well documented. As for groups, some suggest that fewer than five people is safest.)
An interesting graphic has been produced (see below) showing the likelihood of transmission of COVID-19 in various situations. These values reveal when the chance of catching the infection is very low as well as when it is very high. There are other factors involved, of course: viral loads in a particular individual, susceptibility of the people around them, airflow patterns, and even the relative positions of people in relation to each other.
Granted, the situations above are hard to quantify. In the higher-risk situations above, a space of 6 feet or more is especially important. Physical distancing is wise in any situation where groups of people gather, especially indoors, but it’s only a part of the package; hand and respiratory hygiene, masks, disinfection, and other measures must be included to give a more complete picture of risks.
Given the above, lesser restrictions may be appropriate in some circumstances and allow a return to normality for some. It may be a reasonable option in many instances and be best for the economic and psychological well-being of the nation, . Perhaps the best course of action is to allow greater freedom in low-occupancy situations outdoors while always having a mask available to use when needed.