While federal officials have declared the salmonella outbreak linked to Chipotle to be over, the company’s sales continue to struggle.

In a recent regulatory filing, Chipotle reported revenue decreased 6.8 percent to 997.5 million in 2015 compared to 2014 numbers. Between the months of October through December, comparable restaurant sales—a metric that excludes newly opened restaurants—fell 14.6 percent, and according to the Associated Press, Chipotle says January sales tumbled 36 percent at established locations.

“The fourth quarter of 2015 was the most challenging period in Chipotle’s history, but the CDC has now concluded its investigation into the recent E. coli incidents associated with Chipotle. We are pleased to have this behind us and can place our full energies to implementing our enhanced food safety plan that will establish Chipotle as an industry leader in food safety. We are extremely focused on executing this program, which designs layers of redundancy and enhanced safety measures to reduce the food safety risk to a level as near to zero as is possible. By adding these programs to an already strong and proven food culture, we strongly believe that we can establish Chipotle as a leader in food safety just as we have become a leader in our quest for the very best ingredients we can find,” says Steve Ells, founder, chairman and co-CEO of Chipotle.

But the drop in sales isn’t the company’s only problem.

Chipotle now says the previously announced federal investigation into one of its California restaurants has widened. The company must now produce documents and information related to company-wide food safety matters dating back to January 2013.

Chipotle has been undergoing sweeping changes at its restaurants to improve food safety in an attempt to right itself after a multi-state E. coli outbreak was linked to the restaurant chain in November last year. This outbreak was followed by a norovirus incident in Massachusetts that sickened a number of students at Boston College.

The restaurant chain says it has taken aggressive steps to make sure its restaurants are as safe as possible. Specifically, the company conducted deep cleaning at the restaurants linked to this incident, replaced ingredients in those restaurants, changed food preparation procedures and provided all necessary supply chain data to investigators. The Mexican restaurant chain also hired IEH Laboratories and Consulting Group of Seattle, WA to help improve its food safety system.