Another bad number for Chipotle

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Has bad press taken a bite of Chipotle's sales? One firm thinks so.

Just 9.5 percent of consumers visited a Chipotle Mexican Grill restaurant in December, down from 14.1 percent in November, researchers at Bespoke Market Intelligence estimate.

Since Chipotle was linked to food-borne illnesses in late October, analysts have been predicting declining sales at the fast-casual chain. Those predictions were supported by the new report, which estimates a 30 percent decline in visits over the past three months.

Average nationwide monthly visits had ranged from 12 to 16 percent of consumers since July, the research firm estimated in the report Thursday. But in December, visits in the U.S. dropped to 13.5 percent in the Midwest (where traffic can get as high as 20 percent) and 10.4 percent in the West, another popular region for the chain. In areas where the restaurant is less popular, traffic dropped to 7.2 percent in the Northeast and 6.9 percent in the South, according to the report.

Chipotle did not immediately respond to CNBC's request for comment.

California, Illinois, Maryland, Minnesota, New York, Ohio, Oregon, Pennsylvania, Kansas, North Dakota, Washington and Oklahoma were among states linked to at least one strain of E.coli from the chain, according to the Centers for Disease Control and Prevention. A Massachusetts Chipotle also saw a separate outbreak of norovirus this month, the company said.

But all regions saw at least a 4 to 6 percentage point decline in the month of December, by Bespoke's measure.

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Bespoke's calculations hit after a flood of similar data on the company: About half of 21,000 people who answered an unscientific poll on CNBC said they have stopped eating at Chipotle because of the E. coli outbreaks. Bank of America Merrill Lynch analysts Joseph Buckley and Gregory Francfort expect a 25 percent decline in same-store sales in the month of December, according to a recent note.

Chipotle has documented changes to its food preparation in response to the recent outbreaks, including washing and dicing tomatoes in a centralized location, and testing raw meat, cheese and sour cream before restocking restaurants.

"Right now, our highest priority is implementing all of the components of our enhanced food safety program," Chipotle spokesman Chris Arnold told CNBC on Wednesday.