Tensions over this question are rising by the hour. Wary of a long, confined spring, city dwellers are fanning out to vacation rentals, their own second homes, or anywhere else they can find. Airbnb bookings by urban customers traveling to nonurban areas are surging, according to a spokesman. “I can’t just imagine staying in an apartment with a dog and a child when there’s a lawn and space upstate,” said Natasha Schull, 48, a cultural anthropologist at New York University who left Manhattan on Thursday for her home in Delaware County. Worried about a medical condition that predisposes her to pneumonia, she checked the number of ventilators available at the hospital there: 12.

It’s an instant national ethical dilemma, exacerbating already-tense relationships between rich and poor, urban and rural, and, in the case of Hawaii, largely white outsiders and more diverse locals. Who gets to shelter where? Or take the last sack of flour at a small supermarket, or one of those precious upstate ventilators?

Destinations known for welcoming visitors are now closing themselves off. After Ms. Jabola Carolus wrote, Hawaii announced a mandatory 14-day quarantine for all incoming travelers. Southeast Utah has prohibited lodging for nonessential visitors, and Colorado has announced it doesn’t want tourists either. The Outer Banks of North Carolina are shut to nonresidents. The Maine island of North Haven went even further, barring all visitors, including seasonal residents.

History shows that may be the correct call. During the 1918 influenza pandemic, Gunnison, Colo., erected barricades over its highways (“against the world,” in the words of a county physician) and quarantined anyone who entered. Neighboring towns were decimated, but Gunnison’s losses were low. Yerba Buena, an island in San Francisco Bay with a military base and a population of 5,000, locked down for two months with similar results.

Projections of the virus’s spread show the brutal truth: Fellow city dwellers, we pose a threat to everyone else.