WASHINGTON (AP) — Federal officials reported additional cases of E. coli poisoning among people eating at McDonald’s as government investigators searching for the cause of the outbreak identified an “interesting onion grower” in Washington state.

The Food and Drug Administration said 90 people in 13 states have fallen ill during the outbreak, up from 75 at the end of last week. The number of people hospitalized rose by five to 27 people. One death has been linked to the outbreak.

Officials said raw, sliced ​​onions on McDonald’s Quarter Pounder burgers were the likely source of E. coli. McDonald’s said the onions came from a single supplier, California-based Taylor Farms. The company has since recalled the yellow onions it sent to McDonald’s and other restaurant chains.

The FDA said Wednesday that it had begun inspecting Taylor Farm’s processing center in Colorado Springs as well as an “onion grower of interest” in Washington state. The breeder was not named.

More than 80% of people with E. coli surveyed by government investigators reported eating McDonald’s items containing fresh, sliced ​​onions, the FDA found.

McDonald’s announced last week that onions from its Colorado Springs plant had been distributed to about 900 of its restaurants, including some in transportation hubs such as airports. The restaurant chain announced that it would resume service Quarter Pounders in hundreds of its restaurants after testing Beef patties excluded as the source of the outbreak.

The E. coli strain behind the outbreak can cause dangerous diarrhea and lead to kidney failure and other serious problems. According to the Centers for Disease Control and Prevention, it causes about 74,000 infections annually in the United States, leading to more than 2,000 hospitalizations and 61 deaths each year.

FDA officials said Wednesday the current risk of illness is “low as the onions have been recalled and should no longer be available.” They noted that all of the reported cases occurred before Taylor Farms and McDonald’s pulled the onions from the market.

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