A Chipotle Mexican Grill.

(AP Photo/File)

Chipotle posted its first quarterly loss as a public company as it fights to win back diners with free burritos following a series of food scares.

The Mexican food chain says sales fell 29.7 percent at established locations during the first three months of the year.

Chipotle is trying to bounce back after an E. Coli outbreak and norovirus cases that have sent sales plunging. The efforts have included tightening food safety measures, stepped up advertising and coupons for free food. 

"As our sales are on a gradual path to recovery, we remain focused on our mission of changing the way people think about and eat fast food," company founder and chairman Steve Ells, said in a statement.

For the first quarter, Chipotle Mexican Grill Inc. lost $26.4 million, or 88 cents per share. Analysts expected a loss of 98 cents per share, according to FactSet.

Total revenue fell to $834.5 million. Wall Street expected sales of $867.8 million.