People tend to think the terms “natural,” “organic” and “unprocessed” are synonymous with safe and clean food. However, when it comes to microbial contamination of food, these terms are no guarantee that the food is safe. During the past few months, the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention have issued warnings about two major food recalls because of potential contamination with listeria bacteria. However, the contaminated foods are not the typical foods expected to support this type of bacteria.

Question: What foods were recalled?

Answer: Primarily in May, more than 700 various brand-name frozen vegetable and fruit products were recalled. Following that recall, hundreds of products containing sunflower seeds were recalled, and the list continues to grow.

Q: Why were the recalls so extensive?

A: In both cases, very large centralized companies were providing the processing and packaging or raw ingredients for a large number of other companies. Consequently, all products coming from the centralized facilities or made with ingredients from these centralized sources were potentially contaminated. This forced the need to recall extensive amounts of foods that had a chance of being contaminated.

Q: What is listeria?

A: The listeria bacterium of concern is a specific one called lysteria monocytogenes, commonly just referred to as listeria. According to the Food and Drug Administration, a listeria infection can cause healthy individuals to suffer relatively short-term symptoms such as high fever, severe headache, stiffness, nausea, abdominal pain and diarrhea.

However, there is much greater concern for pregnant women. Listeria can cause miscarriages and stillbirths. Older people and anyone with a compromised immune system can experience very serious effects and death in some cases. Even serious brain and nerve damage have been caused by severe listeria infection.

The amount of time it takes for symptoms to develop after ingestion of listeria is quite variable, with symptoms of infection developing any time from two to 70 days after consuming the contaminated food. So, linking a case of listeria infection to the source of the bacteria can be difficult when the contaminated food was eaten two or three weeks ago.

Q: What foods typically harbor listeria?

A: Frozen vegetables and sunflower seeds are not considered likely foods to be contaminated with listeria. The usual suspects are foods like ready-to-eat deli meats and hot dogs, unpasteurized (raw) milk and dairy products, soft cheeses made with unpasteurized milk, refrigerated smoked seafood and raw sprouts.

Frozen vegetables do not contain the protein content usually present in listeria contaminated foods, and sunflower seeds don’t contain the amount of water generally needed by listeria. In addition, roasting of sunflower seeds would kill any listeria on or in the seeds.

Q: How did these atypical frozen vegetables and raw and processed sunflower seeds come to harbor listeria?

A: At this point, we could find no clear answers to this question. Certainly, the affected companies are working hard to figure this out.

To stay abreast of food recalls visit: fda.gov/Safety/Recalls

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.