Things to know about the investigation of E. coli outbreak

Microbiologist Mi Kang works to identify a strain of E. coli from a specimen in a lab at the Washington State Dept. of Health Tuesday, Nov. 3, 2015, in Shoreline, Wash. Chipotle's industry-leading commitment to tracking its ingredients from farm to table is being put to the test by an E. coli outbreak that has sickened at least 37 people as of Tuesday, nearly all of whom ate recently at one of the chain's restaurants in Washington state or Oregon. Scientists also said that they identified the specific microorganism responsible, which they believe was carried on fresh produce such as lettuce or tomatoes. (AP Photo/Elaine Thompson) Microbiologist Mi Kang works to identify a strain of E. coli from a specimen in a lab at the Washington State Dept. of Health Tuesday, Nov. 3, 2015, in Shoreline, Wash. Chipotle's industry-leading commitment to tracking its ingredients from farm to table is being put to the test by an E. coli outbreak that has sickened at least 37 people as of Tuesday, nearly all of whom ate recently at one of the chain's restaurants in Washington state or Oregon. Scientists also said that they identified the specific microorganism responsible, which they believe was carried on fresh produce such as lettuce or tomatoes. (AP Photo/Elaine Thompson)

By Associated Press November 4, 2015 4 min read

SEATTLE (AP) – Thirty-seven people in the Pacific Northwest have fallen ill with E. coli in an outbreak connected to Chipotle Mexican restaurants.

The popular chain of casual restaurants voluntarily closed 43 of its Washington and Oregon locations last week and health officials are scrambling to find the food source of the bacteria.

Here are some things to know about the outbreak:

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WHAT’S BEING DONE TO FIND THE SOURCE?