social distancing primer

From my lovely and talented wife:

The important thing that isn't really coming through to the public, I think, is the relative risk of various behaviors/activities. I worked for 28 years with bucket loads of respiratory pathogens without getting sick. I studied how the microbes caused the diseases once they were transmitted. I didn't study transmission, epidemiology, or public health. But close.

For a respiratory pathogen to cause disease, it has to get into the respiratory tract. The most direct route is breathing in droplets in the air from an infected individual who is secreting them into the fluids of their respiratory tract. Even then, there is a dose effect, so the more of them you breathe in, the more likely you are to get infected. For very rare diseases it only takes a very few microbes, but for most it takes a minimum of several thousand, often millions or more. The number in a single droplet will depend on how many the infected individual you encounter is secreting. The more droplets you inhale, the more your risk. 

Pause. I'm using the term microbe to refer to bacteria, viruses, fungi, and protozoa. Viruses are the smallest of these. They are not capable of moving around on their own. Think of them more like dust particles. So for example, they aren't going to move on their own from one part of a dog to another. The dog might shake them off when it scratches (aerosolizing them), or lick them around however.

So why do we worry about touching our faces?
The second most likely route other than directly through the respiratory tract would be the eyes. Ever notice that if you put eye drops in your eyes, in a few minutes you need to blow your nose? There's a drainage connection there. And it has been scientifically demonstrated that inoculating mice eyes with viruses can establish respiratory infections. So walking into a cloud of droplets without goggles or a mask is an issue. Glasses may help some, but then you might also touch your glasses and face a lot.

Why doesn't wearing a mask in public places help the general public, but is critical for health care workers?  
Think relative risk of running into a cloud of virus when droplets sink so rapidly vs. having infected patients breathe, sneeze, and cough directly on you. So close you can smell their breath for a while, not just for a second.

What about touching your face with virus on your hands?
I think the issue here is that you might rub your face and then rub it into your eyes or nose. And you generally don't wash your face as often as you do your hands.

What about your mouth?
Pretty low risk route of infection if you're talking exclusively about eating food. Viruses entering there would have to survive the saliva and then get swallowed. A tiny tiny tiny amount might be aspirated into your lungs if you choke on your food, but I've never heard that's a validated issue. However, my suspicion is that people often do things like wipe their mouths and otherwise touch their face when they're eating, and that's why they want you to wash your hands before eating to avoid catching a respiratory virus. 

As for social distancing, it's very important to understand the concept of open and closed systems. Astronauts in a space capsule are in a closed system. If you literally never go out of your house, never open your door to anyone or anything (like a pet), no one ever comes in, you get no mail or packages, your house is air tight, and your air is filtered, you'd be in a closed system. Anything else is to some degree an open system. There's a continuum there with most situations being in the gray area. You want to stay towards the closed end of the spectrum as much as possible. Going outside for a walk by yourself or at an appropriate distance of 6 feet from other people is fine, especially since you're in the well ventilated outdoors where if you're lucky there's even sunshine to help inactivate the virus more quickly. Passing them on the sidewalk is very low risk, but don't step in closer than 6 ft for a chat about what's new. The grocery store is still pretty low risk if all you do is pass by people and you're under 60 and have no underlying health conditions. Older people should avoid this and make use of delivery or pick up services. The same goes for drug stores. Check the web or call and ask what accomodations they're making for people in your situation. Invite someone into your house and you're essentially inviting everyone they've had contact with in the last week or two, with that risk going down for shorter time periods or for the longer it's been since they were in contact with an infected person and how well everyone practiced social distancing and hand washing in that gathering. Invite lots of people into a small space, . . . well, duh. 

This virus is already estimated to be far more lethal than the flu, especially for those over 60. Then for every decade over 60 that you get, it's exponentially worse. Exponential, if you don't remember, means that it isn't a linear curve. It steepens rapidly at some point and that point is 60. Over 80 is way way worse. 

Another example of an exponential curve is how at first you hear of only a couple of cases in a particular location, then suddenly it seems to balloon out of control.

So why don't public health officials explain all this better? Beats me. Takes too long. People quit listening. You may have even stopped reading! I just have to trust their experience which seems to be "keep it simple."

Which I probably didn't.