The source of the outbreak was likely slivered onions on McDonald's Quarter Pounder burgers, health officials have said.

The number of E. coli cases linked to onions used by McDonald’s has cracked 100. The Food and Drug Administration said in an update that the number of people sickened by the fast food bacteria outbreak has climbed from 90 to 104.

A deadly E. coli outbreak connected to slivered onions served in McDonald's Quarter Pounder hamburgers across the country has sickened at least 104 people, federal health officials said.