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As promised, something helpful: Shopping!

Updated: May 8

Food! Grocery Shopping!

Ok, there is a video going around with a Doctor, in scrubs, in his kitchen, telling you how to deal with your groceries. That should be enough to tell you that all is not well.


First, the risk of infection from your groceries is really small. The moral of the video is fine, be a little more cautious, but the real risk is not from your groceries, but grocery shopping itself.


The doctor in the video also mixed up two really important studies. The first study showed how long infectious material persists on various surfaces. That was 3 days for plastic and metal, and roughly a day for cardboard. The second study showed that viral RNA could be found on surfaces for up to 17 days. The first study is the important one.


Why? Because only intact virus can infect your cells. The fragmented components of the virus, like just the viral RNA, can do nothing to harm you. You can detect it in lab assays, but it's harmless. The virus cannot reassemble and infect you, just like you can’t put humpty dumpty together again.


Let’s break down the shopping risk down


While shopping, you have the greatest risk of exposure… from other people. We all know this. Physically distance yourself. Stop touching your face! You can’t be infected through your hands, stop touching your face!


Little trick: bring a few Lysol wipes with you and put it on the grocery cart handle. Put your hands on the wipes as you push the cart along. Your hands get sterilized every time you push the cart.


I am super impressed with Market Basket. All staff were wearing gloves. The checkout belt was cleaned between each shopper. Baggers where on every isle which minimized the time you were lining up around others. People sterilizing shopping carts before giving them to you. Seriously, huge thumbs up from me!


Shopping risks:


For item to be contaminated. An infected person had to cough or sneeze on it, or cough or sneeze on their hands, and then touch that item. The first item they touch has the highest viral load, and then the viral load would be diluted with each subsequent item.


Yes, we can’t stop the idiots doing stupid things, but the vast majority of us are doing the right thing. The real risk is very low.


Also, a single viral particle will not cause infection. Each pathogen has an infectious dose. One of the pathogens I work with in my lab is infectious with a single virion. But most other pathogens require much more. For example, with SARS and MERS it was determined that around 1000 viral particles were needed for infection; the expectation is that SARS-COV2 will be the same. So just being exposed doesn’t mean you will infected. You need exposure at the right dose and a susceptible surface…. Nose, eyes, mouth.


Grocery bags: Pose virtually no risk as they are only handled once. Especially, if the bagger is wearing gloves.


Most grocery items also pose virtually no risk. Most people don’t browse cereal or jars pickles. They pick it up and go. Therefore, most items have very few sets of hands on them, even fewer if the grocery store is taking the Market Basket approach and having their stockers wear gloves.


Again, for emphasis: an item needs exposure to, and an infectious dose of, the virus to be of concern to you. If you are worried, bring your shopping home and put them in the pantry for 3 days before unpacking. You are not putting the packaging in your mouth. If you are you are doing it wrong.


To that point, it is not clear you can be infected by eating the virus. i.e. there is no evidence from SARS, MERS, Influenza, or this bug that even if you ‘eat’ the virus, that it can survive the conditions of your gut, or infect your intestinal epithelial cells, or then move to your respiratory cells.


Plastic items. Ok wipe them down if you must… but again, you are not eating the plastic. I assume you are using utensils, and you washed your hands before eating…. Right? The risk is really low.


Refrigerated/freezer items. Now we need to get a little bit more cautious. The item still needs to be contaminated AND have an infectious dose present AND you need to put it in your mouth before you have any chance of getting sick……. But refrigeration and freezing does allow coronaviruses to live little longer on surfaces.


So if you must, wipe down the yogurt container, the drink container etc. Let the cleaner gas-off on your kitchen bench first (let it fully dry), then put it in your fridge.


Produce: this is your biggest risk…. it is still a very small risk, but this is where your risk exists. It is likely that produce have been handled multiple times by multiple people, and with each touch, the risk increases a little.


Produce is also difficult to decontaminate and microbes do persist on their surfaces for quite sometime. As a relevant example, a bovine coronavirus (not this one) can live on lettuce (stored in the fridge) for roughly 10 days. Rinsing the lettuce with water does not decrease the viral load or persistence. I would imagine that many other fruits and vegetables would fall in the same risk category.


It is not immediately clear to me that fruit and vegetable washes contain the ingredients needed to destroy the virus’s integrity. Most commercial fruit and vegetable washes contain various oil extracts that are used to ‘lift’ pesticides off the surface of produce. It is not clear to me if these will serve the purpose of dismantling the viral envelope. Things like oranges, apples, bananas, potatoes, tomatoes you can obviously use a mild dish soap without ruining the produce. For Lettuce, buy a head, and treat the outside leaves as contaminated, peel them off, throw them away (wash your hands), then wash the lettuce as per your usual methods.


Second last point: effective sterilizing agents. Anything contain at least 1% bleach. 60% alcohol. Soap.


Last point: I am seeing people starting to freak out about bringing contaminated shoes in your house. Ok, don't wear shoes in the house. Oh, and don't lick your boots or the floor...

To summarize: Your risk of infection is very very small from groceries (or shoes). Your main worry is other people you walk by or talk too, and that risk is still small in most of our communities right now. It's ok to be diligent, but don't over react. Focus on the bigger risks (other people within your 6ft zone), and drop a little anxiety out of your life with the low risk what if's that seem to be flooding social media.

About the author

Erin S. Bromage, Ph.D., is an Associate Professor of Biology at the University of Massachusetts Dartmouth. Dr. Bromage graduated from the School of Veterinary and Biomedical Sciences James Cook University, Australia where his research focused on the epidemiology of, and immunity to, infectious disease in animals. His Post-Doctoral training was at the College of William and Mary, Virginia Institute of Marine Science in the Comparative Immunology Laboratory of late Dr. Stephen Kaattari.

Dr. Bromage’s research focuses on the evolution of the immune system, the immunological mechanisms responsible for protection from infectious disease, and the design and use of vaccines to control infectious disease in animals. He also focuses on designing diagnostic tools to detect biological and chemical threats in the environment in real-time.

Dr. Bromage joined the Faculty of the University of Massachusetts Dartmouth in 2007 where he teaches courses in Immunology and Infectious disease, including a course this semester on the Ecology of Infectious Disease which focused on the emerging SARS-CoV2 outbreak in China.

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