Amazon said Thursday that nearly 20,000 of its workers have tested positive or been presumed positive for the virus that causes COVID-19. But the online retail behemoth, revealing the data for the first time, said that the infection rate of its employees was well below that seen in the general U.S. population. Amazon said in a corporate blog Thursday that it examined data from March 1 to Sept. 19 on 1.37 million workers at Amazon and Whole Foods Market across the U.S.