For 10 months, you’ve been hearing about how to avoid COVID-19, and what to do if you get infected.

Yet now — as the holidays heighten the desire for and the danger of close contact — confusion seems to be the only thing growing faster than the pandemic. We’ve been hearing it all through Curious Philly, where readers ask questions and our reporters hunt down answers. Hundreds of people have written in to ask about how to quarantine, what isolation means, how to safely socially distance, when they should wear masks and more.

This confusion is understandable. Public health authorities must change their advice as we learn more about the virus, and guidance can’t cover every scenario. Some of the recommendations are unrealistic, given the need to, say, earn a living. What’s more, applying jargon-filled public health advice to real-life situations can be like taking a conditional reasoning exam.

Consider the U.S. Centers for Disease Control and Prevention’s updated definition of “close contact:” “Someone who was within 6 feet of an infected person for a cumulative total of 15 minutes or more over a 24-hour period starting from 2 days before illness onset (or, for asymptomatic patients, 2 days prior to test specimen collection) until the time the patient is isolated.”

Got that? To clarify things (at least a little), let’s revisit some principles, definitions, and previous pandemic installments of Curious Philly.

How do you catch COVID-19? The rules have gotten more complicated.

In March, diagnostic testing was largely unavailable and the virus was assumed to be spread through coughed or sneezed droplets that quickly fall to the ground.

Back then, the CDC advice was straightforward: If you spend at least 15 minutes within 6 feet of an infected person (close contact), then stay home for 14 days (quarantine) because it can take that long after exposure to develop symptoms (the virus’ incubation period). If you develop symptoms while home, then stay away from household members (self-isolate).

The latest expert guidance is more complicated because, well, the coronavirus is more complicated.

» READ MORE: Ask us a question through Curious Philly

The good news: Outdoor transmission turns out to be unusual. Presumably, that’s why protests and civil unrest in the spring did not cause a clear spike in cases. And fears that the germ could be transmitted to someone who touched a contaminated surface (a fomite) also have turned out to be overblown, although frequent hand-washing can’t hurt. (Go ahead with Christmas gift and food exchanges that involve outdoor drop-offs.)

The bad news: Assumptions about big droplets and social distancing have turned out to be simplistic.

The germ can be spread by an infected person — including one who has no symptoms or doesn’t have them yet — in microscopically small particles released into the air by talking, singing, or just exhaling. The virus can waft across a room, carried by air currents or drafts, and be inhaled by a hapless bystander.

And while most people who develop symptoms do so four or five days after exposure to the virus, research has teased out the relationship between exposure, symptoms and infectiousness. The virus takes time to replicate and build up in the body, so the window where you’re most contagious appears to be a day or two before symptoms appear, and for about a week afterward.

This also has implications for molecular diagnostic testing. Studies suggest that in the first four days of infection, molecular tests miss up to two-thirds of infections. After symptoms appear, the rate drops to about 20 percent.

When should you quarantine?

All this helps to explain why the CDC’s updated definition of “close contact,” cited above, is so complicated. It factors in the risks of multiple brief exposures, whether the infected person had symptoms, and whether the infection was confirmed by testing.

» READ MORE: How long can you safely be around someone with the coronavirus? It’s complicated

Guidance on quarantining also has evolved, because staying home for 14 days is often impractical and usually excessive.

Now, the CDC outlines options: End quarantine after 10 days without diagnostic testing if you have had no symptoms. The risk of accidental transmission is low, about 1% to 10%.

» READ MORE: These are the current Philadelphia coronavirus guidelines

If you get a negative test, then quarantine can end after seven days. With this strategy, the risk of transmission is 5% to 12%.

Alas, there are lots of scenarios that the CDC and other authorities don’t explicitly address, so you just have to use your judgment.

For example, suppose you live with someone — say, a child or partner — who had close contact with an infected person. Should you quarantine, too? Experts say quarantine isn’t necessary for people with such “secondary exposure,” unless the person who had close contact tests positive.

Another what-if that Curious Philly has tackled involves whether an infected person can go to an infected friend’s home to hang out together.

“The safest thing is to stay at home,” Patricia Henwood, an emergency medicine physician at Thomas Jefferson University’s Sidney Kimmel Medical College, told reporter Grace Dickinson. “We want people to avoid public transportation or anything else that could cause others to become exposed.”