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Pop quiz: what is Salmonella? If you’ve ever had a run-in with this bacteria, you know it can cause a food-borne illness called salmonellosis, a form of food poisoning. But you may not know that Salmonella bacteria sicken an estimated 1.35 million people and hospitalize 26,500 every year in the United States. What’s more, it kills more total people than any other type of food poisoning.

And Salmonella bacteria can be sneaky — not only by triggering unusual complications, but infecting people in startling ways, says Dr. Elizabeth Hohmann, an infectious disease specialist at Massachusetts General Hospital. One patient she treated showed up with an abdominal aortic aneurysm — a dangerous bulge in the lower section of the body’s largest artery — that looked infected. Testing revealed a culprit some would find surprising: Salmonella.

“It’s just an interesting organism and it can be kind of scary,” she says.

How do people get infected by Salmonella?

Many of the foods Salmonella bacteria lurk in are raw or undercooked. Breaded raw chicken products like nuggets and chicken Kiev are one way it may reach your table. But a variety of foods have been implicated — including organic basil, cantaloupes, ground beef, nut butters, raw cookie dough, eggs, raw or unpasteurized milk, and flour.

Even small pets such as turtles and frogs, along with dog food, have contributed to Salmonella outbreaks in recent years.

You can also become infected by handling contaminated food and spreading the bacteria from your hands to your mouth. Additionally, you can spread it to others on your hands or even on your clothes without becoming sick yourself.

“It’s a bug that’s carried in stool and animal feces and is also present in the environment,” Dr. Hohmann says. “So it can set up shop in lots of different inanimate objects, soils, and machinery, especially in moist environments.”

What symptoms can Salmonella cause?

Most of the time, Salmonella infection leads to gastroenteritis, usually causing just an upset stomach, abdominal cramps, and diarrhea. These symptoms can start as soon as six hours after ingesting the bacteria. Typically, symptoms resolve on their own within two to three days.

Some people have such mild symptoms they’re barely noticeable. “The classic case might be a college student who eats a burrito from a sketchy place, gets sick for a couple of days, gets better, and doesn’t think anything of it,” says Dr. Hohmann.

Sometimes symptoms are more serious, such as severe abdominal cramping and bloody diarrhea, or unexplained high fever and marked fatigue. These symptoms require a call to your doctor.

How is salmonellosis treated?

Most people will get better on their own without any medicines. Replacing lost fluids by sipping water or electrolyte drinks to avoid dehydration will help.

Call a doctor if you have

• diarrhea and a fever higher than 102° F
• diarrhea that doesn’t improve after three days
• bloody stools
• vomiting so severe it prevents you from keeping liquids down.

Treating the infection with medicine comes with an annoying paradox, Dr. Hohmann says. If doctors decide to prescribe antibiotics, the person taking the medicine may shed the organism for longer than if they were never treated. “Then that person may have the opportunity — either through poor personal hygiene, sex, or working as a food worker — to spread it to others,” she explains. “It’s challenging.”

What complications can Salmonella lead to?

Some people get sicker with salmonellosis than others, with seemingly no rhyme or reason. But certain folks are especially vulnerable to serious infection, including:

• adults 65 and older
• pregnant women
• children under 5
• people whose immune systems are weakened by diseases (such as cancer) or treatments (such as immunosuppressing drugs).

A small percentage of those infected can have Salmonella in their blood, which can spread the infection to other parts of the body such as the urinary tract, bones, joints, or central nervous system (brain and spinal fluid).

And, like Dr. Hohmann’s patient with the abdominal aortic aneurysm, on rare occasions Salmonella can lead to unusual blood vessel complications in people who already have atherosclerosis, blockage of the arteries caused by plaque buildup.

“It’s not that common,” she says. “Many physicians are aware of it, so they take special care if Salmonella is found in a person with vascular disease.”

What steps can you take to avoid Salmonella?

While new USDA rules that take effect in 2025 may help fuel recalls of certain foods, we all can take steps to avoid the food poisoning, illness, and hospitalizations that Salmonella exposure can cause.

Dr. Hohmann and the CDC suggest these strategies:

• Using hot water and soap, wash cutting boards or plates on which you cut into raw foods — including vegetables and fruit — before using those surfaces for other purposes. If possible, use separate cutting boards for produce, meat, and fish.
• Refrigerate or freeze foods that are perishable, prepared, or left over within two hours to thwart salmonella growth.
• Always wash hands well with soap and water before preparing food and after contact with animals, using the toilet, or changing diapers.
• If you have a sick pet, take extra care handling its feces and wash your hands thoroughly afterward.

Take additional steps to help more vulnerable people stay healthy:

• Don’t let young children touch high-risk animals, such as turtles, frogs, chickens, or ducks. “And if you’re taking young children to a petting zoo, they should not be petting animals unless you can disinfect their hands immediately afterward,” she says.
• Older adults and those with compromised immune systems should take extra care to wash and cook foods thoroughly.
• People who have had a transplant (such as a kidney transplant) should not keep reptiles or amphibians as pets.

“You hate to make people paranoid, so that we’re washing our lettuce leaves with soap, but it’s worth thinking about these things, particularly if you have people in your household who are susceptible — which is an increasing number of people,” Dr. Hohmann says.

About the Author

Maureen Salamon, Executive Editor, Harvard Women's Health Watch

Maureen Salamon is executive editor of Harvard Women’s Health Watch. She began her career as a newspaper reporter and later covered health and medicine for a wide variety of websites, magazines, and hospitals. Her work has … See Full Bio View all posts by Maureen Salamon

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

It’s undeniable: modern medicine offers ever-expanding ways to heal and prevent disease. But it’s also true that health care can cause harm. One analysis found that about 6% of health care encounters caused preventable harm, leading to thousands of deaths each year. And it’s not just errors that cause trouble. Highly skilled health care providers can cause harm even when they do everything right.

So, how can you reduce your chances of being harmed? Understanding what you can do to lessen the possibility of harm and what’s beyond your control are good first steps.

Whatever happened to “first do no harm”?

Fortunately, it remains a central tenet of medical care. Yet our health care system is complex and fragmented. Each year new medications are added to an ever-growing list, and people live longer with more chronic medical conditions than happened in the past. So in one sense, the successes of modern medical care may contribute to the high rate of health care–related harm.

These harms are often due to our complicated system of health care rather than one individual’s mistake. Harm due to substandard or negligent care is known as medical malpractice. Both health care providers and health care systems have important roles to play in preventing harm to patients.

Are there harms that cannot be prevented?

An enormous volume of scientific research teaches the best ways to diagnose, treat, and prevent disease. Yet people can react to treatments in completely unpredictable ways.

For example, a common and standard antibiotic treatment (think penicillin) can cause anaphylaxis, a life-threatening allergic reaction. Fortunately this is rare, but unless you or your doctor know to avoid it due to past side effects, there’s always a small chance of a severe reaction.

Often less dramatic — yet also unpreventable — harms are:

• Medication side effects. Every medicine comes with potential side effects, such as nausea, sleepiness, or rash.
• Misdiagnosis. Because no one has perfect diagnostic skills, even the most skillful health care provider can be wrong. This can result in unnecessary or delayed treatment.
• Inaccurate test results. Just as no health care provider is perfect, no test is either. False-positive results (indicating an abnormality when none is present) and false-negative results (normal results when disease is present) are common in medical practice. These results can lead to unnecessary treatment or false reassurance.

Which harms can be prevented?

Preventable harms can be dramatically reduced. They’re often due to mistakes that can be caught and corrected. Frequently, it takes a combination of things to go wrong for harm to occur.

The “Swiss cheese model” is often applied here: imagine you’re a fly trying to travel through several chunks of Swiss cheese. (I know it’s an odd scenario, but stick with me here.) It’s impossible to fly through the cheese unless the holes line up just so.

Frequently in health care, several factors must line up for an error to sneak through — for example, giving a hospitalized patient a medication to which they are allergic. For that to happen, the wrong drug has to get past the prescribing doctor, the computerized ordering system, the hospital pharmacist, the nurse giving the medication, and the patient. That’s a lot of layers, so most often an error like this will be caught.

What can you do to avoid preventable harms?

Where do you fit in? In these three scenarios, here’s what you can do to avoid preventable harms.

The problem: Taking medicines you no longer need or more medicines than necessary.

It might not seem like a big deal to keep taking a medicine if it isn’t causing any problems. But all medicines can cause side effects that you’d do better to avoid if you can safely stop taking it or reduce the dose. Plus, harmful interactions can occur if another medicine is added to your list.

What you can do: Make sure you know why you need to take each of your medicines. Ask the providers who prescribe each medicine if it is still necessary to take it or if the dose can be safely reduced. Reducing a dose may reduce the risk of side effects and the likelihood of a harmful interaction.

The problem: Taking the wrong medicine or the wrong dose.

What you can do: At your doctors’ visits, take notes or bring a friend or family member to help you remember medicine instructions. Ask whether you can record the medication instructions your doctor gives you. Take a photo of the instructions you’re given in case you lose the written version. Double-check details of your medicine list with your pharmacist. And ask questions if you’re unsure about the medicines recommended to you.

The problem: Wrong site surgery.

Despite efforts to make this a “never error,” surgery on the wrong part of the body still happens.

What you can do: Make sure you and your surgeon agree on what part of your body and which side requires surgery. Most surgeons now mark the site with a special pen before surgery and ask you to confirm the site by adding your initials. (The ink doesn’t come off easily with skin cleaners applied prior to surgery).

Some of these tips require time or resources that aren’t available to everyone: you might not be able to bring another person with you to medical visits or have a recording device. But asking questions — and getting answers you understand — should be routine.

Where does malpractice fit in?

When the topic of health care–related harm comes up, malpractice may be the first thing you think about. Yet, the approximately 10,000 malpractice payments made each year in the US likely represent only a small portion of all harm related to health care.

There are several reasons for this, including:

• Even when negligent or substandard care occurs, it doesn’t always cause major or long-lasting harm that leads to a malpractice claim.
• Many people who could file malpractice suits elect not to, or may not even realize that they’ve experienced negligent care. Past studies suggest that less than 5% of people experiencing harm related to medical care file malpractice claims.
• Increasingly, health care providers and health care systems accept responsibility for preventable harm occurring on their watch, and offer compensation rather than waiting for a legal claim to be filed.

The bottom line

It’s an unfortunate reality that some harms due to health care are inevitable. But there are steps you can take to avoid preventable harm and lessen the chances that the person harmed is you.

About the Author

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD