California-based True Leaf Farms is recalling 90 cartons of chopped romaine lettuce as it may be contaminated with listeria, though no related illnesses have been reported. Listeria is a frequent cause of U.S. food recalls but concerns over the bacterial contamination are heightened due to an outbreak linked to cantaloupes grown in Colorado, which has already killed 13 people and infected 72 people across 18 states. There is no connection between the lettuce recall and the outbreak tied to cantaloupes, the Food and Drug Administration spokesman Douglas Karas said on Friday.