NEW YORK — Chipotle says it is tightening its food safety standards after its restaurants were linked to dozens of cases of E. coli.

The Mexican food chain said it hired IEH Laboratories in Seattle to help improve its system after reports in late October that linked E. coli cases to its restaurants in Oregon and Washington. Since then, additional cases have been reported in California, Minnesota New York, and Ohio.

The Denver-based chain said the new procedures will include testing of all produce before it is shipped to restaurants, and testing to ensure quality throughout shelf life. It said it will enhance employee training for food safety and handling.

Chris Arnold, a spokesman for Chipotle Mexican Grille Inc., has said the company’s local produce suppliers may not all be able to meet the new standards.

The company has not said how sales have been affected by the E. coli cases.

As of Nov. 19, the Centers for Disease Control and Prevention said 45 people had been infected with the strain of E. coli in six states, and that 43 of them reported eating at Chipotle.