LOS ANGELES (Reuters) - The E. coli outbreak linked to Chipotle Mexican Grill Inc has expanded to nine states, with 47 of the 52 people affected having reported eating at the popular burrito chain.

Shares in Chipotle slid more than 3 percent and then pared losses, down 2.2 percent at $552.74.

The source of the E. coli O26 outbreak is still unknown, the U.S. Centers for Disease Control and Prevention said.

The seven new cases came from California, Illinois, Maryland, Ohio, Pennsylvania, and Washington. Two of the illnesses started in October, and five started in November 2015, suggesting that the outbreak was not as short lived as previously thought.

Of the three most recent illnesses reported in November, only one ill person reported eating at Chipotle in the week before their illness began, CDC said.

(Reporting by Lisa Baertlein in Los Angeles; Editing by David Gregorio)