“Bleak House,” the 1852 novel some consider Dickens’s best, even traces the class lines of an epidemic, revealing its two-sided logic: Its threat is universal, but its real-world damage concentrates on the poor. “It’s the poorest and most socially marginalized people in the novel who disproportionately die of this disease,” she said. “That also has resonance for what we’re seeing now.”

Indeed it does. Among those disproportionately affected are the incarcerated, with outbreaks hitting the Rikers Island jail complex in New York City (more than 850 cases among inmates and staff), the Cook County jail in Chicago (more than 350 cases), and the Oakdale Federal Correctional facility in Louisiana (at least five inmate deaths). Mounting evidence also indicates the virus disproportionately hurts minorities, with data from New York City suggesting blacks and Latinos dying at twice the rate of whites.

The share of poor families doubled up has been rising for at least two decades, said Hope Harvey, a Cornell University sociologist. After the Great Recession, researchers at the Census Bureau found 20 percent of children were living in shared households, including three-generation homes headed by grandparents. In urban areas, as many as half of children live in doubled-up housing by age 9.

In a forthcoming article in the journal Social Problems, Ms. Harvey notes that such arrangements are frequently fraught with conflict and “hidden psychological costs,” as hosts resent the imposition and guests resent loss of control over matters like who comes and goes. “Not being able to control who enters your household would be particularly scary right now,” she said.

Matthew Desmond, a Princeton sociologist who lived among low-income tenants in Milwaukee for his book “Evicted,” said substandard housing posed a threat to mental health even outside a pandemic. “It sends people a message — that their dignity and health aren’t important,” he said.

In addition to having more stable space, the affluent often have greater latitude to remain inside it. They can work on Zoom, shop on Amazon and have gig workers deliver meals. Often lacking credit cards, computers or other conveniences of middle-class life, the needy are accustomed to errands and lines.

“It’s not just the errands that poor people run, it’s the time the errands take,” Mr. Desmond said. “The world tends to be very capricious with poor people’s time. My fear is this will increase their risk of exposure.”