UW virology expert: Avoiding coronavirus a question of probability

Good hygiene has been stressed as a means to avoiding coronavirus infection. So what is it exactly about washing your hands that makes you less susceptible?

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“Everything about a virus spreading like this is a big statistics and probability thing,” said the head of UW Medicine’s Virology Department Dr. Keith Jerome.

Dr. Jerome describes how the likelihood of a single coronavirus particle on a table leading to an infection is “almost nothing.” Where things get risky is when thousands of particles come into play.

“What you’ll see is there’ll be thousands of viral particles on that table, and it’s because somebody sneezed onto your table, right?” he posited. “Your previous guest came, and they sneezed, and now it’s there. Now when you touch it, you might pick up 100 of those. And then you rub your eye, maybe 10 get in there.”

While researchers don’t have an exact estimate, Jerome estimates that after those 10 viral particles get in your eye, “you might have a 50/50 chance” of being infected.

Still, that doesn’t account for scenarios where multiple sneezes could put millions of particles on surfaces.

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“And now you put 1,000 in your eye, then you’re probably going to get sick,” he said. “Everything is sort of this numbers game — this is why every little thing you can do helps.”

That means frequently washing your hands for at least 20 seconds each time, wiping down surfaces you interact with, and avoiding touching your face with your hands.

While these measures may not completely eliminate the risk of infection, it’s all about keeping the probability low.

“Maybe I get rid of 99% [disinfecting my hands],” Dr. Jerome said. “I don’t get rid of every last one, but I’ve lowered my chances, and this is what we need to do.”

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