After the first positive coronavirus test at a Virginia nursing home in mid-March, its administrator said, the staff restricted visitors, conducted temperature checks at the end of every worker’s shift and isolated residents who had tested positive into separate areas.

Even so, there suddenly was another case. Within two weeks, dozens of others inside were falling ill.

Now, about a month after the first case, at least 46 residents are dead at the nursing home, the Canterbury Rehabilitation & Healthcare Center in Richmond — more than a quarter of the facility’s population and one of the highest known death tolls in the United States.