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 an E. coli outbreak 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 Grill Inc., has said the company's local produce suppliers may not all be able to meet the new standards. The company noted that its local produce program accounts for a "relatively small percentage" of the produce it uses, and only runs from around June through October in most parts of the country.

Chipotle has not yet said how sales have been affected by the bad publicity from the E. coli outbreak, but said it will provide a financial update before its presentation at the Bernstein Consumer Summit on Tuesday. In October, the company had forecast sales at established locations would be up in the low- to mid-single digit percentages for 2015.

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.

The ingredient responsible for the illnesses has not yet been determined.

The CDC said on Nov. 20 that it is aware of illnesses starting between Oct. 19 and Nov. 8, but that additional cases could be reported for illnesses that started after Oct. 31.

Chipotle said Friday it tested ingredients before, but it is moving to testing smaller batches and a larger number of samples.

"In testing for pathogens, in many ways you're looking for needles in haystacks. Through this high resolution testing program, we are making the haystacks smaller by working with smaller lots," the company said.

It said that no ingredients that are likely to have been connected to the incident remain in its restaurants or supply system.