Moe Chipotle 17Hollis Johnson/Business Insider
The source of Chipotle's E. coli outbreak might have been tainted Australian beef, according to a new report in The Wall Street Journal.
Citing unidentified sources, Julie Jargon and Jesse Newman report Chipotle has concluded that the Australian beef was the most likely cause.

The report also highlights disagreements between the company and the Centers for Disease Control, which on Monday announced the end to the outbreak and said the source was never identified.
When asked to confirm whether the company believed Australian beef was the source of the outbreak, Chipotle spokesman Chris Arnold said:
We are not going to comment on theories or speculation. The investigation has concluded and no ingredient was identified as the cause.
I'd note that the same article highlights a few theories. In the Northwest, it notes that "local health authorities initially suspected locally sourced produce," according to Washington state epidemiologist Scott Lindquist. And it states that "government officials leaned toward produce."
In the end, investigators were not able to determine a cause.
Chipotle began importing beef from Australia two years ago because it couldn't find enough domestically raised grass-fed beef to meet growing demand, according to Chipotle founder Steve Ells.
"We recently began sourcing some steak from ranches in Southern Australia, which is among the very best places in the world for raising beef cattle entirely on grass," Ells said in a 2014 op-ed article. "The meat produced by these ranchers is 'grass-fed' in the truest sense of the term: The cattle spend their entire lives grazing on pastures or rangelands, eating only grass or forages (by definition, forages are hay and grass — corn is not forage)."
The E. coli outbreak sickened more than 50 people in 11 states between October and December. A second, smaller outbreak linked to a different strain of E. coli sickened five people in three states in December.
The company is making a numerous changes to how it prepares and handles food to avoid another outbreak.
For example, Chipotle is now marinating chopped onions, jalapenos, and cilantro in citrus juice when it makes salsas and guacamole.
The company is also using a new procedure for marinating chicken and steak, "which now happens distinct from and after the preparation of other fresh items" in resealable plastic bags, rather than bowls.