On November 30th, 2015 we learned about

Sneezes and snot spread further than the eye can see

It’s fall! It’s the holidays! It’s… booger season. Boogers and coughs and sneezes are upon us, quite literally if you’re dealing with people who don’t cover their mouth and nose properly. It might not seem like a big deal to sneeze into a space with nobody directly in the line of fire, but germ-transporting fluids do a lot of traveling that you can’t see, allowing them to move much, much farther than anyone had estimated (or wanted to imagine.) New models for droplet movement may show that we not only need to get better about covering our coughs, but also rethink some ventilation systems as well.

Distributed droplets

A solid sneeze can send some obvious moisture flying up to a few meters away, which was long thought to be the worse case scenario for germ transmission. It turns out that this was only a small part of the equation, and that tracking the “ballistics” of a sneeze or cough was missing critical interactions with an invisible “gas cloud” that accompanies unrestrained effluvium. The gas cloud apparently moves more like a belching smokestack, and can carry tiny droplets of spit and mucus much farther than the large droplets you’re likely to see flying through the air. In fact, the smaller the droplet, the farther it’s likely to go thanks to its reduced weight. A droplet at with a 50 micrometer diameter can remain airborne long enough to reach most buildings’ air ducts, at which point they’re able to be distributed to anyone in the vicinity.

Before you attack your sick colleagues who show up at work, a sneeze in the building isn’t a guarantee you’ll be inhaling someone else’s cold virus. As a sneeze or cough cloud travels, it’s usually expanding at the same time. While this obviously raises the risk of pathogens being sucked through the ventilation system, it also actually means the cloud slows to the point where it can’t really support droplets of spittle as well, reducing the risk again. These studies also haven’t specifically modeled how a pathogen would be carried through these airborne fluids, since a sneeze or cough is not completely composed of bacteria and viruses. If we’re lucky, we’ll find that the pathogens expressed in a sneeze aren’t getting a ride in the tinier, most far-flung droplets. All that said, your sick colleagues really should stay at home.

Moving mucus manually

Not every germ is transmitted through airborne vectors, of course. Plenty of germ-laden boogers get around just fine without the help of a sneeze or cough, because your hands get around more than you realize. Simulations with fake runny noses have found that in just 30 minutes, two tablespoons worth of dripping fluids from one’s nose can be distributed across tables, chairs, doorknobs, and even other people. Since this shared snot is basically invisible, it’s great to try to break the chain of transmission by washing your hands whenever you can, even if you don’t have the originating nose in the environment.

Or if you’ve got two drippy kids under seven in your house, just saveĀ up your sick days, because you’ll probably need them.

Source: In the cloud: How coughs and sneezes float farther than you think by Peter Dizikes, MIT News

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