Grocery handling, good bad or ugly?

2020 April 1
by Daniel Lakeland

Apparently this guy’s video is controversial:

I’m going to come right out and say this is a great video, it shows people how to handle objects in a way that minimizes transmission of virus from surfaces. Apparently the controversial part though is where he dumps his oranges in soapy water? Are you kidding me? Everyone should be washing their produce at all times people! Have you ever heard of e-coli?

A frequently heard thing in the “anti” group is something along the lines of “there is zero evidence that xyz”, such as “there is zero evidence that food packaging is a significant source of infection” or “there is zero evidence that washing your food in soapy water is good for you” or whatever. This is typical “Null Hypothesis Significance Testing” type logic… Until we have collected a bunch of data rejecting the “null hypothesis” that “everything is just fine” then we should just “act as if everything is just fine”. Another way to put this is “until enough people have died, you shouldn’t take precautions to protect yourself”. Put that way it’s clearly UTTERLY irresponsible to “debunk” this video using that logic.

What we KNOW is that viruses are particles, essentially complex chemicals, which sit in droplets, which can be viable after floating in the air for 3 hours, which can settle out onto cardboard and be viable for 24 hours, and which can be viable for 3 days on plastic and steel. Guess what your groceries come in? Plastic bags, cardboard boxes, steel cans, plastic jars…

The assay used in the NIH study that established those timelines was to actually elute (wash) the virus off the surface and then infect cells in a dish with it and see how many were infected. It wasn’t just detecting the virus was there, but actually showing that it was active and viable.

So, there’s your evidence. There is *direct* laboratory evidence that the virus *can* be transmitted off the surfaces into cells and infect them.

Whether this is a significant source of infection or not is more or less irrelevant. How do you make a decision as to whether you should spend ~ 1hr every 2 weeks cleaning all your groceries?

Here’s the Bayesian Decision Theory:

Suppose two actions are possible: 1) do nothing, or 2) handle your groceries carefully and wash your fruits and vegetables in dish-soapy water

Costs of (1): probability p0 of getting infected from contaminated surface. We don’t know what p0 is, but leave it as a symbolic quantity for the moment. Let’s just use 0.5% chance of dying if you’re infected as the dominant problem, and a “statistical value of a life” as on the order of 10M dollars… so p0*.005*10000000 = 50000*p0

Cost of (2): probability of getting infected from contaminated surface reduced to p0/100000 perhaps, the same 0.5% chance of dying if you’re infected, plus 1 hr of cleaning time. So cost is 0.5*p0 + w*1 where w is an “hourly wage”. Suppose you are willing to work for a median type wage, 50k/yr. This is 25$/hr. So, what does the probability p0 need to be to “break even”? Ignoring negligible quantities 0.5*p0, we have 50000*p0 = 25 so p0 = .0005. If you think there’s something like a .0005 chance you could transmit virus from your grocery items to your face by “doing nothing” then YOU SHOULD BE CAREFUL and wash your items. For me, I’ll spend some time quarantining my groceries, and washing my produce… I also find it keeps the produce from spoiling and hence lasts longer in storage, so that should go into the “plus” side as well.

As to what to wash your produce with. I’m using sudsy water from dye and fragrance free dish soap (main ingredients: Water, Sodium Lauryl Sulfate…). I’m washing my fruit and veg, and then rinsing it thoroughly. The quantity of soap I’m ingesting is substantially the same as if I hand washed a glass, rinsed it, and then filled it with water and drank it… It’s substantially less than you get from brushing your teeth with a typical toothpaste. If you are afraid of washing your dishes with soap, or of brushing your teeth, then by all means don’t wash your fruit with soap either… For the rest of us, do a good job rinsing just like you’d rinse your glasses or bowls before putting food in them.

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