Times Insider explains who we are and what we do, and delivers behind-the-scenes insights into how our journalism comes together.

Donald G. McNeil Jr. has been covering epidemics for nearly two decades. Times Insider first interviewed him a little over a month ago, when there were 13 confirmed cases of the coronavirus in the United States. Now, more than 7,000 cases have been reported in the U.S. as of Wednesday, and all 50 states are racing to stymie the spread of infection. Mr. McNeil has been reporting on experts’ recommendations for what to do next. He took a break from that to answer a few questions.

What do we know about clusters?

If you get the disease, you are most likely — 75 percent to 80 percent likely — to transmit it to people who are in your household, in your family or people who are in close contact with you at all times. A family in New Rochelle, N.Y., is probably where every single case in New York City came from right now.

The entire outbreak in Seattle leads back to one person. We know that from genetic testing. When it’s all over, you can look at the situation and see what looked like a blanket over the whole city was actually a whole bunch of clusters.