In the second instalment in our series of interviews with McGill experts on COVID-19 issues, Jennifer Ronholm discusses staying safe while shopping for groceries.
Ronholm is an Assistant Professor cross-appointed to the Departments of Animal Science and Food Science and Agricultural Chemistry. Her research interests include using the latest next-generation sequencing techniques to study how the microbiome of food-producing animals affects food quality, as well as how the microbiome of the food we eat affects human health.
How is food at risk of being contaminated in a grocery store? Are there some foods that could be more prone to being contaminated?
The risks of food being contaminated in a grocery store is low to very low, and the risks of actually contracting a COVID-19 infection from consuming food bought from the grocery store is very, very low.
COVID-19 is an enveloped virus, meaning that it is surrounded by a phospholipid, protein, and glycoprotein membrane. These membranes are critical to the virus – it simply cannot infect you if its membrane isn’t mostly intact. However, these viral membranes are very sensitive to desiccation, heat, enzymes, pH, and detergents and therefore, enveloped viruses succumb to the elements relatively quickly when compared to non-enveloped viruses, like norovirus, which are known to spread easily using food as a vector.
There was a study in the New England Journal of Medicine that indicated COVID-19 can remain detectable when deposited on surfaces (stainless steel, plastic, and cardboard) for 72 hours – however, the number of infectious viral particles (required to cause disease) decreases rapidly. After about an hour, only half of the original viral particles remain infectious, and this viable population continues to be cut in half every hour. On cardboard, there was no infectious virus after only 24 hours. The rapid decline in viral viability on surfaces reduces the chances that you will become infected from such surfaces.
To date, there has been no evidence that COVID-19 can be spread by eating food contaminated with the virus. There is a great deal of fear about spreading COVID-19 by eating or touching raw fruits and vegetables that have been touched by others in the grocery store – but there is no evidence that this is happening.
What general rules should be people follow when food shopping?
Never go grocery shopping if you have just returned to Canada from travelling, have been told to self-isolate, or have any of the symptoms of COVID-19.
If you are not immunocompromised or over 60 do not go grocery shopping during the first opening hour of the grocery store. This hour, when the store has been recently cleaned is for the at-risk population.
Always stay two meters away from the other shoppers and workers.
Be quick! If you are going to catch COVID-19 while you are grocery shopping, it will be from another shopper – as opposed to the food, reducing the time you spend in the store reduces your chances of this happening. If it helps, make a list and follow it, don’t browse.
Use the tap option at the check-out to avoid handling cash or having to use the pin-pad.
Use an alcohol-based hand rub before entering the grocery store, wash down the handle of the cart with it, and then wash your hands again before getting into your car.
One person per household. One of my biggest annoyances right now is seeing families shopping at the grocery store. This practice exponentially increases the risk of contracting and spreading the disease.
Should I wear a mask and gloves to the store?
Mask yes, gloves no.
Masks have now been shown to reduce the potential of contracting and spreading the disease and this could be an important part of our long-term strategy of dealing with COVID-19.
Gloves on the other hand are very counterproductive.
When we work in a Biological Safety Level 2 lab, we keep ourselves safe by wearing gloves, but working as if we were not wearing gloves. For example, we wash our hands when we enter the lab, we put our gloves on while we are working, but we change them regularly while we are working. If we spill something on them or move from one area of the lab to the next, we change to a fresh pair of gloves. We have surfaces that are designated as “clean” and when we want to touch one of these surfaces, we do so either with a bare hand or with a new clean set of gloves. When we are ready to leave the lab, we wash our hands very well – as if we were not wearing gloves at all.
These practices ensure that we don’t move contamination from one place to another in the lab and taking our gloves off then washing our hands before we leave the lab is an important strategy to make sure we don’t contaminate other areas of our building with infectious organisms.
Using gloves is only part of an infection prevention strategy – and it must be integrated with other strategies like proper training, hand washing, and adherence to standard operating procedures to be effective infection control.
The average person who wears gloves to the grocery store is not using them properly, and, to be fair, there’s not really a great way of using gloves effectively in this environment. Gloves offer a false sense of security that in all likely hood helps to spread the virus from surface to surface in a grocery store. Washing your hands with soap and water or an alcohol-based sanitizer before you go into the grocery store and again as you are leaving is a FAR more effective strategy.
Is it okay to bring my own reusable bag, or is it better to just get paper or plastic ones and throw them away?
I’m struggling with this question. Humanity has a plastic bag problem that clearly has to be addressed. On the other hand, if everyone is to bring their own bag, society would have to be confident that the bags are getting washed by the patrons prior to each shopping trip or you are potentially creating a new vector that moves around high-traffic areas. The probability of viral spread via reusable shopping bag is extremely low; however, I understand why grocery stores are hesitant to allow their use at the moment. I think using reusable bags a relatively safe practice from a microbiological perspective, however, I understand that the level of anxiety that these bags are causing cashiers may make their use just not worth the environmental benefits at the moment. But after this is over – everyone should go back to using reusable bags.
What about checkout? Should I use cash or credit? Is self-checkout safer?
If self-checkout is available, use it. It keeps the number of cashiers required to a minimum and thus the number of people in a store at a time to a minimum.
Use credit. If you have a tap option on your card, use that to avoid having to touch the pin-pad.
Are the rules in place by most grocery stores enough to counter potential food contamination?
Yes. I think so.
Food is not an effective vector for this virus. Even if the theoretical foodborne pathway exists – which I’m not convinced it does, it is not being reported as being the cause of many new infections. The most dangerous thing in the grocery store is the other shoppers and the two-meter distancing is very important in this respect.
My only potential improvement on grocery shopping infection control is that when I am shopping, even though I am following the arrows on the floor, it is not possible to maintain two meters of distancing from anyone stocking the shelves in the isles. If grocery stores could close for a few hours a day to restock while people are not shopping, it would make it safer for the workers – but this may not be possible or required.
Should people worry about contamination when ordering take-out, groceries, etc.?
No. If you are maintaining social distancing from the delivery person, there is very little probability of contracting the virus from the actual food.
Is it safer for me to get my groceries delivered, even though there are still people involved in this process?
If you have an underlying condition, this would probably be the safest way of getting groceries. However, if you are washing your hands before and after leaving the grocery store and maintaining social distancing while shopping – going to the grocery store is a relatively safe activity.
Do I need to wipe down surfaces on delivered items and groceries? What cleaning products should be used for each?
No. This is unnecessary.
Although transmission of the virus may occur via surfaces, the probability of actually becoming infected this way is very low.
How should I clean fresh fruits and vegetables?
By running them under a stream of warm clean water. Do not use soap on fruits and vegetables, as these products contain chemicals which themselves could make you sick if you ingest them.