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.

It is the fourth listeria-related food recall since Colorado's Jensen Farms voluntarily recalled cantaloupes linked to the outbreak on September 14. Only one of the four subsequent recalls -- of cantaloupes by Kansas food processor Carol's Cuts LLC -- was related to the outbreak.

True Leaf Farms, a processing arm of Salinas, California-based Church Brothers LLC, is voluntarily recalling romaine that was shipped between September 12 and 13 to a food service distributor in Oregon, who further sent it to at least two other states, Washington and Idaho, the company said in a release posted on the FDA website.

The two-pound bags also made their way to Alaska, according to the state's Department of Environmental Conservation.

The romaine lettuce affected by the recall has a September 29 use-by date, the company said in the release. Church Brothers was not immediately available for comment.

Any time we find listeria in food we would consider that food adulterated and ask for a recall, Karas said in an email. The finding of listeria in romaine lettuce was a result of an FDA research program to understand the prevalence of listeria in fresh produce, particularly lettuce and leafy greens.

Listeria rarely causes serious illness. For it to do so, the organism needs to get onto the food and grow to levels where it can cause disease. Because it can grow at low temperatures, that can happen anywhere along the food chain.

Listeria outbreaks are usually associated with deli meats, unpasteurized cheeses and smoked refrigerated seafood products, rather than fresh produce.

Previous food recalls this month included Queso Fresco's Del Bueno Casero Fresh Cheese in Washington state, Publix Super Markets' spinach dip in Florida and Fine Mexican Food Products Inc's avocado pulp and halves in California.