The Chipotle chain voluntarily shut down 43 restaurants in Washington State and Oregon over the weekend after health authorities began investigating an E. coli outbreak.

Health authorities are investigating 19 cases of illness related to the bacteria in Washington and three cases in Oregon, involving an unknown type of food. Eight people have been admitted to the hospital, officials said. No one has died.

“There have been links made to six restaurants in the Seattle and Portland areas,” said Chris Arnold, the communications director for Chipotle, in an emailed statement on Monday. “We have closed 43 restaurants in those markets out of an abundance of caution.”

The Oregon Health Authority said in a statement over the weekend that the infection affected people who ate at Chipotle outlets between Oct. 14 and 23.