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The Difference Between Terms Like 'Airborne Spread' And 'Droplet Spread'


We hear it called the invisible enemy, but scientists are literally looking hard at the coronavirus, measuring the droplets that carry it from person to person and trying to capture so-called airborne spread. Turns out those are different things - at least to a scientist.

JOSHUA SANTARPIA: Droplet spread is like the sort of droplets that you see from a sneeze or a cough - you know, what you might feel if someone coughed on you, whereas airborne spread would be the small particles that you don't necessarily see or know that are there.

GARCIA-NAVARRO: That's Joshua Santarpia, who teaches pathology and microbiology at the University of Nebraska Medical Center. Researchers point to a couple of cases - one at a choir practice in Washington state, the other at a restaurant in Guangzhou, China - as examples of the virus spreading not just a couple of feet from a sneeze or a cough but long distances through the air.

SANTARPIA: Which means that it would be small particles that can be caught in drafts and air currents and moved over distances that you might not obviously expect - kind of move more like smoke than like droplets.

GARCIA-NAVARRO: At the choir practice in Washington state, we saw people who were social distancing, but many managed to get infected.

SANTARPIA: Yeah. That's - I mean, social distancing is an effective practice in sort of casual contact where - you know, with someone you don't know as you're walking by on the street. If you put, you know, a significant number of people - whether they're 6 feet apart or 10 feet apart or 3 feet apart - inside a room together for a long period of time, the probability that transmission is going to occur in that scenario gets higher.

GARCIA-NAVARRO: Is that the same thing that was shown at a restaurant in Guangzhou? What was different there?

SANTARPIA: They'd suspected that it was through the ventilation, which would be, like, much more significant, maybe indicate much smaller particles. There was that recent Nature article also from China which indicated that they found viral RNA and particles that were smaller than a micron. Those two pieces of data kind of match up.

GARCIA-NAVARRO: As the country opens up, how should people be thinking about mask-wearing and social distancing? You know, are cloth masks and 6-feet distance helpful? Can you go to a restaurant?

SANTARPIA: If you're going to a restaurant, for instance, maskwear's probably not in your best interest because you can't wear it while you're eating. And the more you take it on and off or mess with it because you are trying to eat, the more likely you are to create a potential contamination event for yourself. And, in fact, bringing the mask into the restaurant might create its own hazard.

GARCIA-NAVARRO: What about reusing N-95 masks - something that my husband does?

SANTARPIA: It's become a thing that we have to do. It is never something I would have ever recommended before. And in the early days of the outbreak, it hurt me both to throw them away at the end of an activity and also to keep them because the last thing I want to do is keep that thing around because it's dirty. You know, the idea is you're done with your shift. You take it off. You throw it away. That was how they were developed. Now, mask reuse - there's data out there that suggests that, you know, on porous surfaces, coronavirus doesn't live for more than about a day. So if you have a handful of masks and you can cycle them every few days, that's probably a better scenario than picking up the same mask multiple times a day, you know, or day after day after day and then - until it wears out and throwing it out. Other studies that are unpublished yet - you put it out in the sun - it's likely to die a little faster. So, you know, there are lots of things I think that you can do because we're all in a position where we have to reuse masks, whether they're made to be reusable or not, that put us in a position to have to make decisions that I wouldn't normally suggest anyone make. We're working on - and have been since the beginning - a variety of techniques to improve mask reuse both in the hospital and for the general public. And, hopefully, some of that will come to fruition soon, as well.

GARCIA-NAVARRO: That's Joshua Santarpia. He teaches pathology and microbiology at the University of Nebraska Medical Center. Thank you very much.

SANTARPIA: Thank you. Transcript provided by NPR, Copyright NPR.