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  • Writer's pictureP.K. Peterson

For Crying Out Loud: Salmonella in Onions!

“Life is like an onion. You peel it off one layer at a time, and sometimes you weep.”

- Carl Sandburg, American poet, biographer, and journalist

The Centers for Disease Control says that there are 76 million cases of food poisoning in the United States every year, 350,000 hospitalizations, and 5,000 deaths. Is that a lot or a little? Well, it depends on how you look at it.

- Marion Nestle, Professor of Nutrition, Food Studies, and Public Health, New York University

In August, an outbreak of salmonellosis began in the U.S. By October, it had spread through 37 states, sickened at least 652 people, and put 129 in the hospital. On October 20 the Centers for Disease Control and Prevention (CDC) announced that it had found the culprit—red, white, and yellow onions imported from Chihuahua, Mexico had carried the germ Salmonella to unwitting Americans. The bacterial infection salmonellosis is the focus of this week’s Germ Gems post.

What everyone should know about salmonellosis. “Salmonellosis” is the leading cause of bacterial infection of the gastrointestinal tract in the U.S. It is also referred to as Salmonella gastroenteritis or Salmonella food poisoning. There are two species, six subspecies and 2,600 serotypes of Salmonella. The serotype S. oranienburg is the cause of the current outbreak.

Salmonella can be found in a variety of foods, including chicken, beef, pork, eggs, fruits, vegetables, and even processed foods. When compared with other food sources, onions are relatively uncommon vehicles for causing outbreaks of salmonella. According to the CDC, onions can become contaminated at any point in the food supply chain—while growing in the fields, during processing or distribution, or when they're being prepared in a restaurant or home. In 2020, more than one thousand people were sickened after eating contaminated onions. In that outbreak, the CDC identified S. newport as the serotype and found that the distributer Thomson International of Bakersfield, California was the origin. The CDC is still investigating the source of contamination of the onions in the current outbreak. In the meantime, it may be helpful to know if any cases of salmonellosis were identified in your state (23 Minnesotans were sickened)—this information can be found on the CDC’s website.

Two of the wholesale vendors that distribute onions in the U.S., ProSource and Keeler Family Farms, have already issued recalls of their products. If you have red, white, or yellow onions stored in your pantry labeled from Mexico or from either of these vendors, dispose of them. If you’ve eaten fresh red, white, or yellow onions in the past week and you’re sick with diarrhea accompanied by other symptoms such as fever, vomiting, or stomach cramps contact your doctor.

The bigger picture (foodborne illness). Salmonella is just one of a very large group of microbes (bacteria, viruses, parasites, fungi, and prions) and toxins that cause “foodborne illness.” The CDC estimates that each year in the U.S. 48 million people get sick, 128,000 are hospitalized, and 3,000 die from foodborne illnesses. In the case of salmonellosis, the overall mortality rate is less than 1%, but in nursing home outbreaks the mortality rate can be up to 70 times higher.

Diarrhea (defined medically as three or more watery or loose bowel movements a day) is one of the most common health problems affecting people of all ages. It is a salient clinical feature of most foodborne illnesses, including salmonellosis. It is estimated that most adults have four episodes of diarrhea each year and that approximately 179 million cases of acute gastroenteritis (AGE) occur annually in the U.S.

Fortunately, most of these episodes of diarrhea are relatively mild, and most people just “guts them out” at home without seeing a doctor. If you or a loved one develops diarrhea, when should you consider contacting your healthcare provider? My suggestion is contact your doctor if you have diarrhea with any of the following associated symptoms: high fever (that is temperatures over 101F [38.3C]); blood in your stools; severe abdominal pains; or evidence of dehydration. Prompt contact with a healthcare provider should be considered if you or your loved one is at either end of the age spectrum.

Prevention of salmonellosis. The following food preparation measures may be helpful in preventing Salmonella, as well as many of the other myriad causes of AGE from originating in your kitchen:

  • Wash your hands thoroughly with soap, especially after using the bathroom and before food preparation;

  • Don’t share kitchen utensils, plates, or towels if someone in your household is sick;

  • Don’t eat raw meats or eggs or undercooked foods; and

  • Wash fruits and vegetables thoroughly.

In addition to these hygiene techniques, properly freezing or refrigerating foods prevents virtually all bacteria from growing, and heating food sufficiently kills almost all pathogens.

There are also innovative measures to prevent foodborne pathogens from even making it to your kitchen that are worth knowing about. As I discussed in the June 10, 2020 Germ Gems post, “Viruses That Eat Bacteria: Fighting Fire with Fire,” in 2006, the U.S. Food & Drug Administration (FDA) and U.S. Department of Agriculture approved several phage products for the treatment of foods. Phages are viruses that are found everywhere in the environment. They are totally safe, unless, that is, you’re a bacterium that can become infected and killed by them. One such phage product currently awaiting FDA approval is SalmoFresh; it targets Salmonella in poultry and other foods.

A second highly successful way to rid foods of Salmonella, as well as many other bacterial and other types of pathogens, is irradiation. At low doses, irradiation extends a product’s shelf life. At higher doses, this process kills molds, bacteria, and other potentially harmful microbes. Considerable scientific research over the past five decades indicates that food irradiation is a safe and highly effective form of food processing. The U.S. government endorses the use of food irradiation, but disappointingly, it has not educated the public not only about its safety but also about its benefits.

In the U.S. consumers fear that food irradiation will adversely affect their health and mutate and/or change the taste of food. Neither is true. A longtime advocate of food irradiation, Dr. Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, blames an “anti-science movement” for public resistance to food irradiation. His view is: “Not using irradiation is the single greatest public health failure of the last part of the 20th century in America.”

Sadly, with so many other infectious diseases demanding urgent attention (COVID-19 among them), it’s unlikely that either phage therapy or food irradiation is going to be prioritized any time soon. But if this were to happen, it would likely trim the load of foodborne illnesses cases in the U.S. to a much more manageable number.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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