Over the weekend, a nightmarish scenario unfolded in a Seattle suburb, with the announcement that the coronavirus had struck a nursing home. The outbreak, leaving seven dead and eight others ill through Wednesday morning, exposed the great vulnerability of the nation’s nursing homes and assisted living facilities, and the 2.5 million Americans who live in them.

These institutions have been under increasing scrutiny in recent years for a unique role they play in inflaming epidemics. Research shows these homes can be poorly staffed and plagued by lax infection-control practices, and that residents frequently cycle to and from hospitals, bringing germs back and forth.

Now, public health experts fear these facilities could become central to the rise and spread of the novel coronavirus. Statistics from China show that the infection caused by the virus, called Covid-19, kills nearly 15 percent of people over 80 years old who have it and 8 percent of people in their 70s — the very population that makes up more than half the population of these homes.

“We have to prepare for the inevitability that there are going to be facilities like the one in Washington where you’re going to have the virus and have it move rapidly through nursing homes and assisted living facilities,” said Dr. David Dosa, a geriatrician and professor of medicine at Brown University, where he studies disaster preparedness.