Panera is facing a lawsuit after a Natick family found a dollop of peanut butter inside a grilled cheese they ordered for their six-year-old daughter with a serious peanut allergy.

Elissa and John Russo filed the suit against Panera and a group of franchises in New England in Middlesex Superior Court last week, stemming from the Jan. 28 incident, the Boston Globe reported.

John Russo told the Globe that their daughter was diagnosed with a peanut allergy around the age of 18 months; the family has been vigilant since, often explaining her condition at restaurants, and always bringing epinephrine pens with them.

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On Jan. 28, Elissa Russo ordered her daughter a grilled cheese through Panera's online ordering system. She noted in two separate places that the sandwich was for a child with a peanut allergy.

But it wasn't until after their daughter had bitten into the sandwich did the family discover its secret ingredient.

John Russo told the Globe the incident was especially shocking because they had given two warnings in their order. The family's suit charges that the restaurant "engaged in unfair and deceptive business practices by adding peanut butter to the plaintiff's grilled cheese sandwich knowing that [she] has a life-threatening peanut allergy."

The girl didn't immediately show symptoms, but was panicking, asking her parents if she was going to die. She wasn't discharged from the hospital until the next day.

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In a phone call with the Natick location, John Russo said a manager blamed the incident on a "language" issue, suggesting a worker with limited English saw the peanut notation and added the ingredient to the sandwich. 

But Russo said that was "no excuse," and unfathomable. 

According to the lawsuit, a similar incident happened about a month later at the Wayland Panera, when a child suffered an anaphylactic reaction after eating a grilled cheese sandwich with peanut butter.

Panera's website notes that its locations cannot guarantee its items are allergen-free due to shared equipment, but an attorney for the Russo family says this is not an incident of accidental contamination.