Is shopping low risk for COVID?
October 26, 2020 10:48 AM   Subscribe

I'm trying to understand why shopping is often listed as a low risk activity for COVID exposure. If COVID is transmissible by aerosol as the science seems to indicate, shouldn't spending time in an indoor, semi-ventilated space be considered a higher risk? Or is it because of the lower concentration of people and expected spacing and movement (compared to say, sitting in a restaurant)?
posted by roaring beast to Science & Nature (25 answers total) 3 users marked this as a favorite
 
It has to do with time and proximity. If you are going to the grocery store, for example, you can be efficient - get what you need and get out straight away - and it is easy to move away from most people you encounter. You can also wear a mask for the whole time. In a restaurant, you are sitting closer to other people for a longer period of time, removing your mask to eat and drink. You may also need to use the loo, which is by definition a very closed space.
posted by nkknkk at 10:56 AM on October 26, 2020 [14 favorites]


Cynically, it's a smoke screen. Anything they could do to fix the ventilation in retail space is too expensive. And reducing access significantly would be too much of an imposition on the culture. So, sure it's safe. Same as poultry plants.

Same as the EPA said ground zero air was safe.

Mask up, be quick. Don't stand under the outflow vent by the door.
posted by j_curiouser at 11:00 AM on October 26, 2020 [11 favorites]


The FAQs on Protecting Yourself from COVID-19 Aerosol Transmission document links to a National Geographic calculator to Measure the risk of airborne COVID-19 in your office, classroom, or bus ride.

Unfortunately the calculator doesn't include grocery shopping or restaurant scenarios specifically, but if you compare "An indoor gathering" with the sliders set to no masks, which seems to me is kind of like a restaurant, and "A bus ride" with the sliders set to wearing masks, which seems to me more like a not-crowded store, you can see that the risk levels are night and day different. The indoor situations where people have masks, have lots of space, and aren't having conversations end up looking pretty safe.
posted by john hadron collider at 11:17 AM on October 26, 2020 [3 favorites]


People talk a lot more at restaurants and can't wear a mask while eating.
posted by Candleman at 11:18 AM on October 26, 2020 [7 favorites]


Shopping is often listed as a low-risk activity for Covid because:

(1) The lists you're seeing take activities, and they rank them. There is no comparison on these lists of "not shopping" or "not leaving home," so the ranking of shopping as a low risk activity is compared against other risky activities, not activities that actually carry little to no risk, like getting your groceries delivered. Think about activities on a scale of 1-100, where 1 is "almost no risk" and 100 is "you will absolutely get Covid." Just making up numbers here, but if shopping is a 61 and eating at a restaurant is a 79 and attending a kissing contest is a 98, of course shopping looks low risk! But they're not including getting groceries delivered at a 6, or having a video call with your cousin, at 1.

(2) Risk valuation in good public health communication has two factors: "perfect use" and "typical use." If you use a condom, for example, perfect use means you have a 98% success rate at preventing pregnancy, but typical use means an 85% success rate at preventing pregnancy. A big difference. Activities that are qualified as less risky in terms of Covid seem to be lab tested stats, so are counting perfect use. So if going shopping is "very safe," the stats are built on the presumption that you and everyone you encounter will be wearing masks correctly, no one sick being out and about, everyone washing hands, etc. In reality, that's almost never the case, and safety stats make things look safer than they are because of human fallibility.

So basically, these are logic errors. The reason shopping is listed as "less risky" is because of human logical fallacy.
posted by juniperesque at 11:20 AM on October 26, 2020 [13 favorites]


Shopping at a store where everyone is wearing a mask and leaving once they finish shopping is obviously safer than going to a restaurant and taking off your mask to sit and eat and drink and talk to other people. It’s not as safe as never leaving your home and only getting things delivered, but it is safer than bars, restaurants, concerts and Trump rallies. I’d even say it is pretty “low risk” compared to those activities.
posted by cakelite at 11:35 AM on October 26, 2020 [8 favorites]


Your contact with others is quite short, so even if a person is infected, you aren't in proximity to them for very long.
Masks are required.
Low risk is relative and is not no risk.

Also, food shopping is essential. I found food delivery/ pickup to be unsatisfactory. When I shop, I try to buy lots of food so I won't have to do it again for 2 weeks. Now I have tons of canned goods and am trying to use that up and avoid shopping.
posted by theora55 at 11:38 AM on October 26, 2020 [5 favorites]


I think it's a relative risk here. Eating indoors in a restaurant is relatively more risky than going shopping indoors, because people need to take off their masks to eat, and may be consuming alcohol.

In addition, going grocery shopping is an essential activity in a way that eating in a restaurant isn't. It took some time for the science of aerosols to become known, so our earliest classifications of risk were based on best information available at the time. But it does check out that permitting only essential activities (like grocery shopping) combined with a responsible public health policy can manage the spread of COVID-19. And while contract tracing has been a disaster in the U.S., surely other countries with more robust contact tracing systems would have found evidence of grocery shopping being a major threat.
posted by oceano at 11:38 AM on October 26, 2020 [4 favorites]


In addition to the comments above, if I'm at a restaurant, I'm usually there with a person and we are talking/laughing throughout the meal. At a store, I may ask where something is located, or thank the person checking out my purchase, but there's a lot less aerosol creation in general.
posted by tchemgrrl at 11:39 AM on October 26, 2020 [1 favorite]


The growing realization is that Covid is transmitted between households to a large degree in superspreader events. Since it apparently takes more than one virus particle to start an infection, you need all the factors together: infected people in close quarters, inside with poor ventilation, without masks, talking/breathing heavily for an extended period of time. The grocery store doesn't expose anyone for a long period, it's brief exposures to a bunch of people. Hopefully there are masks, and for the most part people don't talk. With those three factors, you have greatly reduced risk. Restaurants have all the risk factors, as far as I can see.

The other aspect is that acquiring food and sanitary supplies is, to use an overloaded term, necessary. If you don't do it, some delivery person or warehouse worker has to. So there's a sense in which it isn't low low risk but in terms of risk and necessity it is.
posted by wnissen at 11:40 AM on October 26, 2020 [8 favorites]


So there's a sense in which it isn't low low risk but in terms of risk and necessity it is.

I think that's a more realistic practical view. A useful comment.

I, personally, am of the belief that it didn't have to be this way. Too much of a distraction, maybe.
posted by j_curiouser at 11:45 AM on October 26, 2020


Think about the coronavirus expelled by an infectious person like a smoker's smoke. If someone lit up in the opposite corner of a grocery store, you likely wouldn't even notice. And by the time you got to that corner, the smoke likely would have dispersed quite a bit given the size of the average grocery store and the height of its ceilings, and the smoker would potentially be gone and not generating any more smoke. Even if you did notice the smoke, it may not be enough to trigger your asthma.

Now imagine that same smoker sitting in a restaurant. Restaurants tend to be smaller with lower ceilings, so the concentration of smoke will be higher, even on the other side of the dining area. If you're sitting at the next table, you're in their smoke cloud for an extended amount of time, because you're sitting and dining. The smoke is much more likely to trigger your asthma in that setting.

As others have said, add to that the fact that people wear masks less in restaurants (because they're eating and drinking) and talk more (which expels more coronavirus), and you can see why grocery shopping is low risk compared to indoor dining.

In terms of decision making, I prefer the multiple dimension risk/reward graphs that show things like shopping in the low risk/high reward quadrant vs bars and concerts in the high risk/low reward quadrant. (e.g.)
posted by natabat at 11:53 AM on October 26, 2020 [11 favorites]


(1) The lists you're seeing take activities, and they rank them. There is no comparison on these lists of "not shopping" or "not leaving home," so the ranking of shopping as a low risk activity is compared against other risky activities, not activities that actually carry little to no risk, like getting your groceries delivered. Think about activities on a scale of 1-100, where 1 is "almost no risk" and 100 is "you will absolutely get Covid." Just making up numbers here, but if shopping is a 61 and eating at a restaurant is a 79 and attending a kissing contest is a 98, of course shopping looks low risk! But they're not including getting groceries delivered at a 6, or having a video call with your cousin, at 1.


This is not really correct. The spread of covid requires both time and proximity to someone infected, and yes, activities like 'stay at home' are included in the risk profiles. As far as the current data can show, about 35% of spouses caring for a known covid patient get covid, children and others in the same house hold is about 5%. So short of working in a hospital caring for many covid patients we have a baseline of risk.

Time = approximately 15 minutes of moderate exposure, which means someone may have covid but they didn't cough directly on you. If they cough on you or kiss, then time goes from 15 minutes to 0 minutes, ie doesn't matter.
Proximity = distance from a potential covid patient. 6 feet is a close enough guess. Most stores have decreased the number of shoppers so this distance is feasible.

Then activities are ranked in danger compared to that.

If you compare time and proximity, you do not spend the majority of your time in a grocery store standing next to another person not in your family. Maybe you walk down a few aisles randomly crossing the same person. Maybe you stand in line next to time for 15 minutes at a long checkout line. This is where proximity comes in. Stay 6 feet away and you are safer. Wear a mask and that time increases.

Compare this to a restaurant: you are in close proximity to a small number of people for generally longer than 15 minutes. You are opening your mouth, possibly passing off drinks or plates to be coughed on by a server. You can't eat with a mask. This is a higher risk.

Compare to a bar: you are in very close proximity. High degrees of close contact. Possible kissing. You can't drink with a mask. High proximity, high time exposure.

BTW: there are no known cases of store shoppers spreading covid using masks and distancing that I have seen. Store workers yes, but not shoppers.
posted by The_Vegetables at 12:09 PM on October 26, 2020 [13 favorites]


BTW: there are no known cases of store shoppers spreading covid using masks and distancing that I have seen. Store workers yes, but not shoppers.
I'm not sure if absence of evidence is evidence of absence here. In my county, over 50% of detected cases are "community transmission" (ie: we were unable to determine where you got it via contact tracing). That doesn't mean that shoppers are getting it at stores, but I don't think we can rule it out.
posted by Alterscape at 1:16 PM on October 26, 2020 [5 favorites]


In my county, over 50% of detected cases are "community transmission" (ie: we were unable to determine where you got it via contact tracing). That doesn't mean that shoppers are getting it at stores, but I don't think we can rule it out.

Maybe not, but considering that people have been shopping at relatively consistent rates throughout covid and that shopping has no correlation with the number of cases, I think you can discount it, even if discounting does not mean ruling it out.
posted by The_Vegetables at 1:34 PM on October 26, 2020 [8 favorites]


People don't talk constantly with no masks on when shopping, so fewer aerosols are generated and spread than, say, in a restaurant, with constant talking, laughing, and no masks.
posted by nouvelle-personne at 3:39 PM on October 26, 2020 [1 favorite]


So, sure it's safe. Same as poultry plants.

No, actually. I appreciate that there is a lot of unknown community spread that has people jumpy, but I think a few points are worth pulling out:

- There's no reason for people to be unmasked in a supermarket (even though some people may be) unlike a place where people are eating, drinking, or taking breaks where they eat/drink/smoke.
- The rankings are relative, not absolute. So it's low risk compared to a lot of other not-smart stuff that people nonetheless do. Which is A LOT of stuff.
- You can stay farther from people at a supermarket than you can at many of the factories where people have been getting COVID
- Earlier in COVID times people were worrying about fomites (i.e. what you can get while touching stuff) on groceries and now they are less worried about that as a vector.
- Air exchange in a supermarket isn't great but many supermarkets have very high ceilings and at least some ventilation
- You are not using a restroom in the supermarket (usually) which makes it different from a workplace

If you are a very at-risk person, then a grocery store may be too unsafe. If you have an average risk profile otherwise, the grocery store is generally considered low risk compared to the other human activities that people are likely to engage in.
posted by jessamyn at 3:47 PM on October 26, 2020 [13 favorites]


One thing I think gets left out of Covid conversations a lot is the HVAC systems of the places we are talking about. Generally, Grocery Stores are housed in modern buildings, that have modern HVAC systems. Modern HVAC systems are made to not only keep air circulating, but to incorporate air from outside of the building into the air circulation. All of these things are important when weighing your risk of catching Covid-19. Some of the earliest releases of information about who caught Covid in office buildings and restaurants were about proximity to AC vents. Additionally, if you consider that grocery stores keep their stores climate controlled to prevent food spoilage, their HVAC systems need to be even better than most regular facilities- these factors most likely keep Covid at bay. Another thing to consider is that people move through grocery stores, they do not congregate in one spot for very long. All of these reasons are why grocery stores are a lower risk than other places.
posted by momochan at 6:52 PM on October 26, 2020 [2 favorites]


One way to think about it is that your risk is a tiny fraction of the risk that grocery employees face. They are there 40 hours a week and you are there probably less than an hour. They are face to face with hundreds of customers a week. You are face to face with maybe only one employee. So your risk is only about one or two percent what employees face.

You can also reduce your risk by going during off hours. Ask employees when the slow times are. Sometimes there is a big line up exactly when the store opens first thing in the morning but it thins out 15 minutes later. The air has had a chance to clear over night.
posted by JackFlash at 8:44 PM on October 26, 2020 [2 favorites]


One other factor is the prevalence of the disease in your community. If you can stock up in times when there is a lower case rate, your risk will be lower than shopping when rates are spiking.

If you want to go to the store when the number of people is lowest, check google maps for a graph of times of day the store is busiest.
posted by yohko at 10:08 PM on October 26, 2020


One thing I think gets left out of Covid conversations a lot is the HVAC systems of the places we are talking about.

I personally think 'air exchange' is either dramatically overstated or still extremely poorly understood when it comes to COVID. COVID first came around in the US in the winter, when people spend way more time in-doors. NYC got hit but the rest of the country's large metro areas was much slower. Florida and other places in the south blossomed in the spring, the south in early July, when people spend measurably more time outdoors. Remember beach closures in the summer? Now it's ramping up again in the summer/autumn when people are returning indoors and grouping more, and A/C use is decreasing.


Not only that, in the US at least, COVID cases are much higher among blacks and Hispanics, who have A/C in their homes at about 25% less AC prevalence in a subset of cities by race - blacks have central AC at rates 50% lower than whites in the studied midwest cities which is the opposite of what you would expect to see if breathing circulated air was a big driver of COVID spread.

I'm not saying that HVAC systems have no concerns with spread, but if you want to identify COVID spread (and avoid COVID), then you could use race, income, and other factors way before getting down the list to 'spend time in A/C'.
posted by The_Vegetables at 8:27 AM on October 27, 2020


Or is it because of the lower concentration of people and expected spacing and movement (compared to say, sitting in a restaurant)?

Correct, plus:
- masks stay on, unlike in a restaurant
- talking is minimal, unlike in a restaurant (this is a biggie and often overlooked. Look at the data on Japan's mass transit. Everyone packed in like sardines but masks on, no talking = no aerosols being spread around.)
posted by fingersandtoes at 8:59 AM on October 27, 2020


I don't know how big a piece of it this is, compared with time in proximity, or even just time in the store at all, and some of the other answers already given. But we're talking about food shopping being lower-risk and e.g. restaurants being higher-risk. There'll be exceptions, but this would suggest that a higher percentage of diners are comfortable with or for other reasons engage in higher-risk activities than food shoppers (overlap notwithstanding). It suggests to me that if you could do a study, you'd find that the average diner engages in more higher-risk activities than the average food shopper (higher risk here, in fairness, meaning 'having a couple of friends over the house' in some cases, not necessarily 'having a maskless reception introducing a Supreme Court nominee').

This could be offset by other factors -- small restaurant vs. big supermarket, or having a corner table in a place where the exemplary HVAC means your risk is limited mostly to whether the next table is positive and whether you need to navigate to the bathroom while you're there, hypothetically, compared with a situation where a larger number of other food shoppers are continually crossing your path, a few of them with masks not covering their noses. But it seems like it would play at least a small part.
posted by troywestfield at 9:08 AM on October 27, 2020 [1 favorite]


I just want to respond to what The Vegetables wrote above, implying that HVAC is interchangeable with AC. The point I was trying to make was that large buildings with Modern HVAC systems- which included Heating, Ventilation, *and* Air Conditioning, have systems in place that not only heat and cool a building, but also add ventilation that creates air exchange that brings in outdoor (fresh) air no matter what the system is using. Outdated or Old HVAC systems were generally created with the concept of air recirculating in a building to heat or cool it, with the building being as air tight as possible- which as we all can imagine would be terrible for catching Covid. Additionally, modern HVAC systems also have air filtration systems to filter air- and scientists researching Covid have recommended specific filters to help combat Covid. My point about grocery stores is that most areas in the United States where grocery stores have followed the capitalist model of building a fully new building, or full renovating the space every 10-15 years, generally have the most up to date HVAC systems in them, and therefore are safer spaces then smaller restaurants or school buildings that have not been updated in 25-50 years.
posted by momochan at 2:23 PM on October 27, 2020 [1 favorite]


These articles model eating at a restaurant and socializing in bars.
posted by oceano at 7:59 PM on October 29, 2020


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