Salinas, California-based  lettuce grower River Ranch Fresh Foods has issued a recall for bagged salads after detecting listeria contamination.  The contaminated packages were distributed in several states, including California.

Listeria bacteria is found in soil, water and animal feces. Humans typically are infected by consuming:

– Raw vegetables that have been contaminated from the soil or from contaminated manure used as fertilizer

– Infected meat

– Unpasteurized milk or foods made with unpasteurized milk

– Certain processed foods — such as soft cheeses, hot dogs and deli meats that have been contaminated after processing

Symptoms of listeria infection include high fever, headache and neck stiffness. Infants, the elderly and those with weakened immune systems are at risk of becoming severely ill from the bacteria.