The level of debt in America’s corporate sector amounts to 75 percent of the country’s gross domestic product, breaking the previous record set in 2008. Among large American companies, debt burdens are precariously high in the auto, hospitality and transportation sectors — industries taking a direct hit from the coronavirus.

Hidden within the $16 trillion corporate debt market are many potential troublemakers, including the zombies. They are the natural spawn of a long period of record low interest rates, which has sent investors on a restless hunt for debt products that offer higher reward, with higher risk. Zombies now account for 16 percent of all the publicly traded companies in the United States, and more than 10 percent in Europe, according to the Bank for International Settlements, the bank for central banks. A look at the data reveals that zombies are especially prevalent in commodity industries like mining, coal and oil, which may spell upheavals to come for the shale oil industry, now a critical driver of the American economy.

Zombies are not the only potential source of trouble. To avoid regulations imposed on public companies since 2008, many have gone private in deals that typically saddle the company with huge debts. The average American company owned by a private equity firm has debts equal to six times its annual earnings, a level twice what ratings agencies consider “junk.”

Signs of debt stress are now multiplying in industries impacted by the coronavirus, including transportation and leisure, auto and, perhaps worst of all, oil. Slammed on one side by fear that the coronavirus will collapse demand, and on the other by fears of a supply glut, oil prices have fallen to below $35 a barrel — far too low for many oil companies to meet their debt and interest payments.

Though investors always demand higher returns to buy bonds issued by financially shaky companies, the premium they demand on U.S. junk debt has nearly doubled since mid-February. By last week the premium they demand on the junk debt of oil companies was nearing levels seen in a recession.

Though the world has yet to see a virus-induced recession, this is now a rare pandemic. The direct effect on economic activity will be magnified not only by its impact on balky debtors, but also by the impact of failing companies on the bloated financial markets.

When markets fall, millions of investors feel less wealthy and cut back on spending. The economy slows. The bigger markets get, relative to the economy, the larger this negative “wealth effect.” And thanks again to seemingly endless promises of easy money, markets have never been bigger. Since 1980 the global financial markets (mainly stocks and bonds) have quadrupled to four times the size of the global economy, above the previous record highs set in 2008.