Australian beef has been blamed for a mass E. coli outbreak at US fast food chain Chipotle despite authorities finding the cause of the outbreak in 14 states unclear.
The Centre for Disease Control and Prevention reportedly closed their investigation after being unable to pinpoint any of the 64 ingredients used by the restaurants as the likely culprit.
Publicly the Mexican food chain stated the same, but privately beef supplied by Australian farmers since 2014 has been determined as the cause, the Wall Street Journal has reported.
"Chipotle concluded the E. coli was most likely from contaminated Australian beef," the Wall Street Journal said.
The restaurants are continuing to serve Australian beef but have reportedly begun taking additional precautions, including testing the beef for pathogens and implementing measures to avoid staff members directly handling raw meat.
Hundreds of people across the US are believed to have fallen ill after eating contaminated food from Chipotle.
The first outbreaks linked to the chain were reported in July last year and were followed by seven other reports of major outbreaks.
The CDC declared earlier this month it was likely the outbreak was over, and concluded an investigation without identifying the source of the contamination.
