Chipotle Mexican Grill Inc said on Sunday it had closed all its restaurants in two West Coast markets due to a reported outbreak of E. coli bacteria that is being investigated by the company and health authorities.

“After being notified by health department officials in the Seattle and Portland, Oregon, areas that they were investigating approximately 20 cases of E. coli, including people who ate at six of our restaurants in those areas, we immediately closed all of our restaurants in the area out of an abundance of caution,” company spokeswoman Danielle Moore said in an emailed statement.