Chipotle says its sales fell for the fifth straight quarter, as the company struggles to win back customers after an E. coli scare last year.

The burrito chain says sales fell 21.9 percent at established restaurants during the quarter ending Sept. 30. That's worse than the 18.3 percent drop Wall Street analysts expected, according to FactSet.

The company has given out millions of free burritos and launched a three-month loyalty program in June to try to bring customers back. In September, it offered even more freebies: Kids could eat free on Sundays and students could grab free sodas or iced tea with their meals.

Shares of Chipotle Mexican Grill Inc. fell nearly 2 percent after the market closed Tuesday. Chipotle's stock is down about 40 percent in the last year.