Salmonella: No. 1 Cause of Death in Everyday Food, Treatment Dilemmas

Since salmonella’s discovery nearly 150 years ago, humans have tried and failed to eradicate this bacterium.

Illustration by The Epoch Times, Shutterstock

On Nov. 12, 2023, the U.S. Food and Drug Administration (FDA) issued a recall for salmonella-contaminated cantaloupes. Three deaths have been announced over the past month, adding to the hundreds caused by one of the most lethal food poisoning pathogens in the United States.

Since salmonella’s discovery nearly 150 years ago, humans have tried and failed to eradicate this bacterium.

“It is very difficult to eliminate this pathogen from the food chain,” said Aliyar Fouladkhah, associate professor in the Department of Agricultural and Environmental Sciences at Tennessee State University. “Still more than a million people in this country catch this bacteria in a typical year.”

Salmonella: Why Is It So Common in Food?

Salmonella, which looks like a tiny rod with long tails, is the No. 1 cause of hospitalizations and deaths from foodborne illnesses in the United States each year.

It can be found in foods such as meat, eggs, dairy, fresh produce, and even processed food.

There are more than 2,500 variations of salmonella, but not all cause infections.

Many farm animals, especially cattle, pigs, and chickens, can naturally carry salmonella and show no signs of illness. This makes it difficult to fully eradicate the bacteria from meat. In a sense, salmonella in animals is like E. coli in people.

“For example, we talk about E. coli (Escherichia coli), right? We have a significant amount of E. coli moving inside of us. Although some of them can cause significant gut infections, the majority of them are benign,” Amilton de Mello, associate professor of meat science and food safety at the University of Nevada, told The Epoch Times.

More than 25 percent of poultry have salmonella in their gut. In 2019, more than 40 percent of foodborne salmonella infections were caused by chicken, pork, beef, or turkey.

The prevalence of salmonella in meat means that contaminated food is allowed to circulate in the market.

In 2019, over 40 percent of foodborne salmonella infections were caused by chicken, pork, beef, or turkey. Guitar photographer/Shutterstock, Aleksandar Malivuk/Shutterstock

“In the U.S., salmonella is considered an adulterant of ready-to-eat foods, but not [of] raw animal products such as meat and poultry,” Craig Hedberg, professor at the University of Minnesota and co-director of the Minnesota Integrated Food Safety Center of Excellence, told The Epoch Times in an email. “In some countries, specific strains of salmonella are prohibited.”

The U.S. Department of Agriculture (USDA) proposed to declare salmonella an adulterant in breaded and stuffed raw poultry products in August 2022, meaning that these meats wouldn’t be allowed to contain more than a negligible level of salmonella. Whether the proposal will be implemented is still undetermined.

Unlike E. coli, which has been identified to have only seven foodborne infection-causing strains, many salmonella strains may or may not cause disease, making controlling pathogenic strains a heftier problem.

However, the USDA does require manufacturers to inspect their meat routinely. At every inspection, 52 chicken carcasses are examined, and meat batches are considered acceptable only if 13 or fewer carcasses contain salmonella.

While manufacturers producing meat products for schools have a zero tolerance for salmonella contamination, others producing whole-bird, parts and ground products are allowed a tolerance of salmonella varying between 7 percent and 25 percent from lots of 51 to 56 samples.

Contamination of Fresh and Processed Produce

Unlike viruses, bacteria are very hardy and can survive on surfaces, in soil, and in water for more extended periods.

Studies have shown that salmonella can survive in soil and water for more than a year. If fresh produce comes into contact with contaminated water or soil, it can also become infected. More than one-third of salmonella infections are caused by vegetables or fruits.

A good wash with water can remove up to 90 percent of the bacteria on the surface. However, sometimes, the inside of the produce can also become contaminated.

“Let’s say we purchased some strawberries and some cantaloupe to bring them home, lightly rinse them, and consume them. If they are contaminated [inside], we are exposed to those pathogens,” Mr. Fouladkhah said.

Contamination can occur due to a bruise or cut on the surface of fruits and vegetables. Edi Hartlim/Shutterstock, Grossinger/Shutterstock

So how can salmonella enter the produce? Contamination can occur because of a bruise or cut on the surface of fruits and vegetables, including apples, tomatoes, and leafy greens.

“Those locations where injury has occurred can lead to multiplication of microbial populations at the site of injury,” Donald Schaffner, distinguished professor of food science at Rutgers University, wrote to The Epoch Times via email.

In laboratory conditions, salmonella has also been shown to penetrate fresh, undamaged produce, but it’s unclear to what extent this occurs in the real world, he said.

Processed food such as peanut butter and cookie dough can also become contaminated during processing.

“Peanuts can be contaminated during production, and if not properly processed, the contamination remains in the peanut butter,” Mr. Schaffner wrote. “Wheat can be contaminated in the field before or after harvest,” which is how the bacteria could be found in uncooked flour.

Peanut products, including peanut butter, can become contaminated during production. Nordroden/Shutterstock, Mironov Vladimir/Shutterstock

Recalls: The Last Resort

Since salmonella-contaminated food can cause outbreaks, recalling it is a last resort to limit further cases.

Genomic sequencing is used to track the cases, allowing epidemiologists to link cases and trace them back to the common source of infection.

“Let’s say I’m getting sick here in Nashville. Sometimes, someone in Colorado is getting sick with the same strain. In a short amount of time, [epidemiologists] can link them together,” Mr. Fouladkhah said.

Then comes contact tracing and interviewing patients to identify the food in question.

The difficulty of tracking an outbreak varies case by case.

“[Contaminations from] fresh produce might be a little bit more difficult than meat products because there are only a handful of large meat facilities in the country,” Mr. Fouladkhah said.

Depending on the product and how the epidemiological work goes, recalls can be announced as quickly as a few days or as long as weeks and months. However, sometimes the contamination source can’t be found.

Pasteurization Conundrum

Besides meat and produce, eggs are another primary source of salmonella infections, making up almost 7 percent of foodborne illnesses.

The United States has different regulations for salmonella in eggs, which are determined based on whether the eggs are shelled or if they’ve been cracked open.

Shelled eggs don’t have to be pasteurized, while pasteurization is compulsory for eggs used in processed foods. Studies estimate that only 3 percent of shelled eggs are pasteurized.

Pasteurized eggs are moved toward the packaging area at the National Pasteurized Eggs (NPE) processing facility on March 22, 2006, in Lansing, Illinois. Scott Olson/Getty Images

Two regulatory agencies govern shelled versus unshelled eggs, each with its own guidelines.

The USDA regulates unshelled eggs, while the FDA regulates shelled.

Mr. Fouladkhah said each agency’s size and abilities dictate its regulations.

For food companies whose products are under USDA jurisdiction, an on-site USDA inspector ensures that food is processed according to regulations during manufacturing.

“If they are under the FDA jurisdiction, they have less frequent inspections,” Mr. Fouladkhah said.

This is partly because the FDA oversees a much larger number of operations, so it doesn’t have as many inspectors available for more frequent inspections.

To Treat or Not to Treat

Diagnosing and treating salmonella infections can be challenging since the symptoms are similar to those of other foodborne illnesses and stomach bugs.

The most reliable way to diagnose a salmonella infection is by culturing stool samples, which can take at least two or three days. Only by culturing salmonella can doctors know which serotype patients are infected with and which antibiotics will be suitable.

Culturing the bacteria is the most reliable way to diagnose a salmonella infection. Arif Biswas/Shutterstock

Genomic sequencing is much faster and can detect salmonella within hours. However, it can’t detect the exact serotype and, therefore, doesn’t help guide treatment.

After the serotype is determined, doctors must decide whether the patient should be treated with antibiotics.

In healthy individuals, salmonella infections generally resolve without treatment. However, people who are immunocompromised or have underlying health problems may need antibiotics to clear the bacteria.

Healthy patients given antibiotics can actually cause retention of salmonella, leading to further spread of infection or chronic infections.

A 2000 Cochrane Review found that patients with antibiotic regimens tested negative during the first week of treatment, but relapses were also more frequent among this cohort. A subsequent review of salmonella treatments found that some patients reported worsened symptoms after antibiotic treatment.

Salmonella bacteria invade a human cell. NIAID

Another 2016 study following 1,047 patients with persistent salmonella infections found that more than 90 percent were immunocompetent, and those who took antibiotic treatments had three times greater odds of having persistent infections.

“We’ve known for a long time that treating people who are not that sick [with antibiotics] can actually prolong the intestinal carriage and delay clearance of the salmonella,” Dr. Elizabeth Hohmann, infectious disease physician at the Massachusetts General Hospital, whose research focuses on gastrointestinal infections and gut microbiome, told The Epoch Times.

Some studies have suggested that salmonella persistence may be caused by the bacteria going dormant in the gut. It may also be caused by antibiotics damaging the good bacteria in the gut, according to Dr. Hohmann.

If people have mild symptoms, aren’t too young or old, don’t have multiple medical comorbidities or planted prosthetic devices, and are getting better, “it’s typically not recommended that they be treated,” she said.

In some cases, delayed or lack of treatment can cause salmonella to invade the blood, causing bacteremia. This can lead to systemic inflammation and even death. Immunocompromised people are particularly at risk of bacteremia, although it can occur in healthy patients.

Certain salmonella serotypes are more invasive than others.

“When you’re seeing the patient for the first time, you can’t know that. So these decisions are not easy to make at times, and they do rely a lot on the judgment of the clinician,” Dr. Hohmann said.

US Salmonella Control

Despite frequent notices of recalls of salmonella-contaminated food driving a perception of prevalent salmonella outbreaks, food safety experts argue that the United States is doing quite well in controlling infection cases.

The average incidence of salmonella infection is about 15 per 100,000 in the United States. The European Union in 2021 had a notification rate of 15.7 per 100,000.

In 2021, Australia reported a notification rate of 42 cases per 100,000 people. Canada reported an annual incidence rate of 19.7 per 100,000 in 2019.

Some countries, like Japan and Sweden, have a meager rate of salmonella infections. Japan reported 2.4 cases per 100,000 residents in 2011, whereas Sweden had an incidence rate of 6.3 per 100,000 in 2022.

Mr. Fouladkhah said comparing the United States to many of these smaller developed countries would be unfair.

“[In the United States,] there are great diversities state by state, with both large and smaller facilities,” he said.

Mr. de Mello attributed the differences to antimicrobials used during food processing. For example, it’s common practice in the United States to clean meat with chlorine and other disinfectants. This was banned in Europe in 1997 because of the concern that it may be used to make up for poor hygiene practices and animal welfare issues.

Electron micrograph of a bacteriophage. The United States uses bacteriophages, viruses that kill bacteria, in meat processing. Image Source Trading Ltd/Shutterstock

The United States also uses bacteriophages, viruses that kill bacteria, in meat processing. Research by Mr. de Mello, published in Meat Science, has shown that bacteriophage reduced salmonella in meat by 90 percent.

Nevertheless, it remains a relatively niche intervention.

“Bacteriophage is highly effective, but they don’t use that commonly in the meat industry,” Mr. Fouladkhah said.