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MIAMI (CBSMiami) — Chipotle Mexican Grill has been served with a subpoena by a federal grand jury in connection to illnesses at one of its California restaurants.

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The company announced Wednesday that U.S. Attorney’s Office and the Food and Drug Administration are investigating a norovirus outbreak that occurred over the summer in the state.

Last month, a restaurant in Boston shut down after 30 students got sick and that number eventually climbed to at least 141 students.

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In November, the Centers for Disease Control and Prevention said nine states reported an E. Coli outbreak in which 52 people fell sick from eating at Chipotle.

43 stores were closed down in the Pacific Northwest.

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Chipotle’s sales dropped in the fourth quarter of 2015.