The number of E. coli cases linked to McDonald’s Quarter Pounders has increased, US health officials said this week.

It was announced on Wednesday by the US Food and Drug Administration that at least 90 confirmed cases of E. coli strain O157:H7 have now been identified in 13 states, and hospitalizations have risen to 27.

Two victims developed hemolytic uremic syndrome, a serious condition that can cause kidney failure. One death was linked to the outbreak from the beginning.

Meanwhile, sliced ​​onions previously served on McDonald’s Quarter Pounder burgers were named as a probable source of contaminationaccording to the FDA and US Centers for Disease Control and Prevention.

The FDA said it launched inspections at Taylor Farms’ Colorado processing plant, which supplied recalled onions to McDonald’s, and an unnamed onion farm in Washington state.

McDonald’s promptly removed the sliced ​​onions from the affected locations and stopped sourcing from the Taylor Farms facility in Colorado indefinitely.

The FDA noted that diced onions used at McDonald’s “were not implicated in this outbreak.”

Where is the E. coli outbreak?

After removing Quarter Pounders from the menu at 900 of its restaurants after the outbreak was discovered, McDonald’s will resume serving hamburgers in affected areas this week.

But the sandwiches won’t be served with onions at those locations.

The areas affected by the E. coli outbreak are in Colorado, Kansas and Wyoming, as well as parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, Oklahoma and Utah, US health officials said.