McDonald’s shares plunged as much as 6% Wednesday after an outbreak of E. coli that sickened almost 50 people and killed one was linked to the Golden Arches’ famous Quarter Pounder hamburgers.The largest burger chain in the world saw its shares drop from $314.70 a share at Tuesday’s closing to $299.61 a share by late Wednesday morning.“This public health scare is the last thing McDonald’s needs given that it’s already been struggling to drive growth,” said Susannah Streeter, head of money and markets at Har ...