Monday marked another stage in the global battle to outwit the new coronavirus, as reported infections in the rest of the world overtook those in China. Millions of people in Europe and the United States began holing up at home amid rapid-fire border closures announced by one nation after the other. Stocks tumbled even further in Monday morning trading on Wall Street as the economic fallout of the outbreak widened. The S&P 500 lost more than 7% at the open, triggering a 15-minute halt to trading, and losses deepened after trading resumed, mirroring sharp falls elsewhere around the world.