A quite similar term, "social distance", also existed for a long time (dating to the 1920s), referring to social-status-distance rather than physical-separation-or-hygiene-in-public-and-social-contects.
The epidemiological term seems to date to 2006 and a US Government planning document.
I've found the term vague, confusing, and inconsistent with established usage.
There are also many cultures that are renowned for being “socially distant”, even if they’re very small, very compact, and very public transit-reliant.
This seems like globalizing a term that was originally very western- (and particularly English-speaking-) centric.
How do you do physical distancing within your home? Eat meals alone? Don't share cups/plates? Wear gloves for doorknobs? I feel like there's currently no solution for this.
You can't avoid a lot of that, given the physical constraints within a home. This just means it's even more critical for people who live with others to do physical distancing so they don't bring it home.
Football stadiums, convention centers, that sort of thing. They set up a bunch of cots and people laid there to recover. If you started to deteriorate, they sent you to an actual hospital.
There's talk about doing this maybe with all of the empty hotel rooms in NY.
> How do you do physical distancing within your home? Eat meals alone? Don't share cups/plates? Wear gloves for doorknobs? I feel like there's currently no solution for this.
I don't think you really need to. Say the average household size is 3. If everybody locks down just within their household, the maximum spread of infection is 3x the current level. If that's done early enough, things will be pretty much fine in terms of hospital capacity, etc. Though if somebody in your household is especially at risk, they may want to stay in a separate room for a few days until it's clear that everybody else is safe.
I am hoping we have good science behind the “1.5 metre” distance rule...
Does anyone have links to videos that show how breath swirls around, especially in outdoor areas? I guess I could get some pollen and try and model it myself!
I’ve listened to an interview with a virologist (is that the word?) She said that there have been many studies in how droplets move when people sneeze and cough. These studies have been done with different sized droplets. She said that 1m is probably already enough, so that 1.5m is the recommendation.
>The threshold distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route.
It seems that depending on conditions < 2m is a good practical threshold for droplet transmission. Probably more if person is really sick.
The goal is to get as small dose viruses at once as possible. Immune system can usually fight off small exposure.
Sometimes even healthy people who inhale huge amount of viruses into their lungs at at once can get very seriously sick because their immune system struggles with the large sudden attack and goes into overdrive.
This shows that large droplets don’t travel, but that small (< 4.7nm - accurate?) do travel e.g. ~10% particles measured at 6 feet.
Issue 1: drop off rates look to rude approximation to be r^2. The were measuring a point source. If you are standing in a line of people, you need to integrate along the line, and inter-person distance needs to be increased. A field of people (supermarket) needs something different...
Issue 2: large droplets should travel further if outdoors? (turbulent air)
Issue 3: cigarette smoke is a familiar visual indicator: “cigarette smoke particle mainly distributed in the size range 0.1 to 1.0 micron”. Think about how the smoke exhaled by someone travels (ignore how smoke travels from end of cigarette due to heated air).
Nope. The higher the dose you get at any given time, the likelier it is that enough virions will establish footholds in enough cells to overwhelm the local protective response and survive to replicate.
To be clear, that's not an antibody-mediated immune response, which takes longer. Before then, cells penetrated by virus particles often undergo apoptosis, self-destructing to defend the larger organism by preventing the virus from hijacking the cell's machinery to reproduce itself. Sometimes the virus wins, though. So the more particles you're exposed to, the higher the odds that one or more will establish itself and start making you sick.
For more, see e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2517702/ - but if you don't want that level of detail, you can just think of it as "flattening the curve" on an individual scale, and not really go far wrong.
edit: More accurate use of "immune" now that I'm not commenting from a phone with a small screen. Apoptosis isn't initiated by the immune system, but rather within the affected cell itself, and doesn't only occur in response to viral invasion; many types of cellular injury or damage can cause it, including most of the ways that a cell can become precancerous. (Which happens a lot more often than you might think! But most such cells self-destruct before they can give rise to a tumor.)
> This is interesting, i had always thought it was binary, either you get infected or you don't
IIRC, some vaccines work by exposing the person to a tiny amount of virus so that their immune system can "learn" how to fight that particular type of virus.
Do we have any idea how this changes outdoors? I could see it being worse because the wind spreads virus farther or better because it gets diluted quicker.
Honestly it's probably both. Each breath will contain some amount of virus baring particles at a relatively low velocity. Each cough and sneeze will release more virus baring particles with a greater distribution of sizes and velocity.
It's key to remember that the 1.5m (or whatever rule) isn't about making you 100% safe, it's about sufficiently reducing risk. For example, if standing at normal (2-3 feet) distance has a 1% chance getting you infected, and at 5-6 feet it has a 0.1% chance of getting you infected, that's a huge win.
Perhaps simplistic advice is better than no advice.
The way I see it, the advice we're given is not so much geared towards safety of the individual as to slowing the spread of the infection, basically lowering R0. They could say five meters, but that is impractical, so would be universally ignored. So the idea would be to settle for a recommended distance that seems practical, while lowering the risk of infection to a reasonable degree.
Let's face it: Whether you or I get through this unharmed, is of little or no significance compared to what will happen on a larger scale.
As noted in the bright yellow box at the top of the page, this is an unreviewed, and as you note unreplicated, preprint. Don't place too much weight on it.
Also note that it describes aerosol concentrations as "undetectable" in the patient-use areas where samples were collected.
It doesn't seem like a rule that's based on any sort of science about infection rates. The primary considerations seem to be to make it an easily understandable number, far but not so far you feel like you're shouting at people from a distance.
You might need to use small droplets rather than pollen to get relevant results. The Ars Technica summary of COVID-19 might have a reference for that distance figure; IIRC it was based on the distance that most droplets travel before falling.
“Cloud, fog and mist droplets are very small. Their mean diameter is typically only 10-15 micron (1 micron = 1/1000 mm) but in any one cloud the individual drops range greatly in size from 1 to 100 micron dia.“
Fog also has very high humidity (otherwise it would evaporate), so any study that shows lower transmission of the virus in high relative humidity environments has relevance to anyone that assumes droplet evaporation matters? https://www.accuweather.com/en/health-wellness/new-study-say...
This is kind of interesting. Check figure C.2. The behavior of droplets depends on size, but they all either evaporate or fall to the ground within 4.5 seconds. Knowing this has made me feel better about better about walking a dozen feet behind somebody outside.
If evaporation matters, then transmission rates should depend strongly upon humidity. However, there are studies saying transmission rates decrease with relative humidity. Maybe drying is irrelevant, or maybe there is another factor, or maybe the studies are wrong.
I distinctly remember reading recently that it's absolute, not relative, humidity that counts. The article did not give a reason, nor can I remember the source (sorry).
If we assume the same volume of air is expelled in the examples, then that video just looks sciency, and really doesn’t show us anything actionable (apart from don’t sneeze directly at people, duhhh!).
Also, why cough onto the back of the hand? What cultures is that normal?
I prefer the term Physical Avoidance. but yeah, I think it’s a better yet than social distancing although “social distancing” has better recognition because “social” is more “au currant” as a term.
[1] Kelso J,Milne G,Kelly H (2009) Simulation suggests that rapid activation of social distancing can arrest epidemic development due to a novel strain of influenza. BMC Public Health 9: 117.
I found an earlier reference (May 2006) in the context of transmission prevention here [0]:
> The idea that within a week or two of a pandemic's initiation we could quench it by saturating a ring of at-risk population with oseltamivir, achieving 90% coverage and high compliance, and at the same time impose movement restrictions and social distancing—all this depending on the causal virus having an Ro <2·0—is simply fanciful.
I don't know, but I suspect its popularity of late might have something to do with its use in the 2011 movie Contagion, which has seen much reference in recent days.
I think social distance was better than physical distance because social distance to me suggest static clustering.
It's not a bit deal for you to be physically close to people as long as it's very few people and that cluster doesn't intermingle with other clusters. A household is a good example of a physically close cluster that can be socially distance from other clusters.
The key thing is to try to prevent contamination from cluster to cluster.
Also, "social distance warrior" is a more amusing way to describe those people on social media that can't stop posting about social distancing.
What about a more visual description, like "safety circle"?
When I was a Boy Scout learning to use an axe, they called the danger zone within reach of the axe the "blood circle". A bit overwrought, but it certainly stuck in my mind. I think they say "safety circle" now.
You can. You just can't justify it as "But the WHO told me to!"
(That's not just snark. I have a compromised immune system. I have been enjoying giving people withering looks and having them walk the hell away and stop breathing on me and what not. That's never really worked before.)
Quarantine does not accurately describe what the WHO is asking people to do. Quarantine is when you take potentially infected people and isolate them from the rest of the population, allowing all the unexposed people to go about their days normally.
Edit: Updated to clarify that quarantine is about potential and not actual infection.
No, quarantine is when you isolate a group of people for a period of time. It is used to see if they MIGHT be sick, or when people are known to be sick, to allow it to burn out.
The original usage was specifically when ships were required to stay in port for 40 days before being allowed to dock, so that any sickness could burn itself out or be apparent.
Thanks for the correction. You're right that quarantine does not require knowing whether people are actually infected. However, it's still about isolating specific people or things to protect the rest of the population and not about asking the whole population to change its behavior.
The Wikipedia article for cordon sanitaire [1] mentions quarantine as an alternative way to handle disease spread.
> Public health specialists have included cordon sanitaire along with quarantine and medical isolation as "nonpharmaceutical interventions" designed to prevent the transmission of microbial pathogens through social distancing.
