This blog post from a professor of epidemiology has some interesting logic. I don’t know this person, but they are a professor at a reputable university and I give their opinion some weight based on that. You can review their credentials and decide for yourself.

I took microbiology as a graduate student in environmental engineering, and I’ve done just a bit of microbial risk assessment since then. Which in no way qualifies me as an expert on covid-19. But this post did help me to think about some things harkening back to my classes, which are almost entirely absent from other media sources I am reading. In my classes and my professional work, there is a logic of dose response – you have to ingest a certain amount of material, and it has to contain a certain amount of a pathogen, for you to get sick. This usually has to do with small amounts of fecal matter present in the environment or water in my case, and the consequence typically is a bout of gastrointestinal distress curable with rest and fluids, although pretty much any disease is more dangerous to the very old, the very young, and the very sick.

That was a long preamble. You should read the blog post. But here is the brief summary:

• If someone coughs or sneezes directly in your face, you are likely to get infected.
• If you spend significant time indoors in a place where an infected person has recently coughed or sneezed, you are likely to get infected.
• Other than that, you are not likely to get infected from someone breathing or even talking to you as you briefly pass on the street. You would need to talk to that person for at least 5-10 minutes to be likely to take in enough virus to get infected. That is just not very likely if you pass someone while walking, jogging, or biking. The advice of my local and state health departments is consistent with these facts. The behavior of people I observe in my neighborhood is not consistent with these facts. My behavior is consistent with these facts, even if other people in my neighborhood choose to have opinions that are not consistent with the known facts, and to try to impose those opinions on me.
• Now, if you are indoors for awhile in a place where a lot of people are talking and breathing, and someone is infected, your odds of getting infected are high. This is why offices and schools are closed.
• The bigger the crowd in the indoor space you are in, the more likely someone is infected. This is why conferences, religious services, sporting events, and Disney World are shut down.
• So, people are getting infected when they have to be indoors around a lot of other people for a period of time, like in warehouses and meatpacking plants and unfortunately nursing homes. They are getting infected when they choose to attend large group events they don’t need to attend, like parades or worship services. And finally, they are getting infected when a family member goes out, gets infected, and brings it home.