Bill Ackman, founder and CEO of hedge fund Pershing Square Capital Management, posted his very first tweet on Wednesday from a Chipotle Mexican Grill (CMG) - Get Report

Ackman's Pershing Square is the largest holder of Chipotle shares, and his debut on Twitter (TWTR) - Get Report  comes just a day after the company's stock fell as much as 7.5% after reports surfaced of a store closure where multiple customers fell ill.

Pershing Square lost about $74 million at midday Tuesday. Chipotle shares are slightly higher in afternoon trading.

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