A record surge in coronavirus cases is pushing hospitals to the brink in the border cities of El Paso and Ciudad Juarez, confronting health officials in Texas and Mexico with twin disasters in the tightly knit metropolitan area of 3 million people.

Health officials are blaming the spike on family gatherings, multiple generations living in the same household and younger people going out to shop or conduct business.

The crisis — part of a deadly comeback by the virus across nearly the entire U.S. — has created one of the most desperate hot spots in North America and underscored how intricately c...