The closure of 43 Chipotle Mexican Grill restaurants in the Pacific Northwest following an E. coli outbreak led to a dramatic decline in the brand's consumer perception, according to the latest YouGov BrandIndex survey.

The consumer perception research firm, which surveys 4,300 adults every weekday, said Monday that Chipotle's "buzz score" fell to -19, a steep decline. Surveyed consumers' perception of the Denver-based fast-casual chain hit its lowest level in at least 14 months.

To calculate the "buzz score," BrandIndex asks thousands of consumers about hundreds of brands and asks them whether they have heard anything positive or negative about the brands through advertising, marketing or word of mouth over the previous two weeks. The score is calculated on a scale between negative 100 and positive 100.

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