CDC reports 9th death in listeria outbreak tied to Boar's Head deli meat. What to know about foodborne illnesses and their symptoms.

Six more people have died in an ongoing listeria outbreak linked to sliced deli meat from Boar's Head, bringing the total number of deaths to nine individuals, the Centers for Disease Control and Prevention reported. The patients ranged in age from 32 to 94 years old, with deaths occurring in Florida, Tennessee, New Mexico, South Carolina, Illinois, New Jersey and Virginia. As of Aug. 28, 57 people have been hospitalized since the beginning of the outbreak, which has been reported in 18 states.

Boar's Head expanded its recall in July to include an additional 7 million pounds of deli meat amid ongoing listeria concerns, according to the U.S. Department of Agriculture (USDA) officials. The 71 ready-to-eat products included in the recall originated from a Virginia plant between May 10 and July 29 and include both packaged meats and meat intended to be sliced at delis. Liverwurst, ham, beef salami, bologna and other products are affected.

The expanded recall was in addition to an earlier Boar's Head recall of 207,528 pounds of deli meat products announced last week. That recall came after a sample of Boar's Head liverwurst from a Maryland store tested positive for listeria; the company then recalled other meats produced on the same line and same day (June 27).

Foodborne illnesses are shockingly common in the United States. The CDC says that about 48 million people get sick from foodborne diseases every year. Here's a guide to everything to know about these illnesses, from symptoms to treatment.

Listeria

What it is: A disease-causing bacteria called listeria monocytogenes. It can survive and grow under refrigeration. The disease people develop after eating food contaminated with this bacteria is called listeriosis.

What the symptoms are: Mild symptoms of listeriosis include fever, muscle aches, nausea, vomiting and diarrhea, while symptoms for the more severe form of listeriosis include headache, stiff neck, confusion, loss of balance and convulsions, according to the Food and Drug Administration (FDA).

What experts need you to know: “Listeria has the unfortunate property to grow under refrigeration temperatures, which is uncommon for foodborne illness,” Dr. Albert Shaw tells Yahoo Life. Shaw is an infectious diseases specialist and professor of medicine at Yale School of Medicine. Shaw added: “It can contaminate any food really, but we see outbreaks in raw fruits and vegetables, as well as improperly heated hot dogs and things like deli meats. Unpasteurized milk or soft cheeses, especially Brie and queso that are made with potentially unpasteurized ingredients, have been associated with outbreaks in the past.”

While listeriosis symptoms can typically be treated at home, Dr. Julie Parsonnet notes that the disease can be serious in certain individuals. Parsonnet is a professor of infectious diseases at Stanford University School of Medicine. “Pregnant women are at risk because the bacteria can get into the bloodstream and the placenta, and there’s a high risk of fetal loss due to the infection,” she tells Yahoo Life. “The elderly can also get listeria in their blood and their brain, causing meningitis. It’s not a common cause of disease, but among the foodborne illnesses, listeria is one of the more common causes of death.”

Salmonella

What it is: A group of bacteria that can cause gastrointestinal illness. It’s typically associated with meat and poultry as well as undercooked eggs, but dairy products, fruits and leafy greens can also be contaminated.

What the symptoms are: Gastrointestinal illness, which includes diarrhea, fever and stomach cramps. More severe illnesses associated with salmonella include high fever, lethargy, a rash and blood in the urine or stool, according to the FDA.

What experts need you to know: In the U.S., poultry and eggs are the most common sources of salmonella, says Parsonnet. You can typically avoid the bacteria by cooking your food. It’s also important to avoid cross contamination while preparing food, making sure that raw ingredients don’t touch anything you will be consuming.

Shaw says that for those with a normal immune system, salmonella typically runs its course in two to three days. Though most people recover at home, Parsonnet says it’s possible to see “severe illness in people who are immunocompromised or have sickle cell anemia.”

E. coli

What it is: A bacteria that lives in the intestines of people and animals, and is known as Escherichia coli, or E. coli. Though it is harmless while in the gut, ingesting certain types of E. coli — such as E. coli O157:H7 — can cause severe gastrointestinal issues, according to the Mayo Clinic. One way E. coli is spread is when feces contaminate food and water. Since animals can potentially carry pathogenic E. coli, touching animals, such as at a petting zoo, can potentially put you at risk.

What the symptoms are: Stomach issues include severe cramping, diarrhea, nausea and vomiting. Fever is also common. In extreme cases, E. coli may lead to a type of kidney failure called hemolytic uremic syndrome (HUS), or the development of high blood pressure, chronic kidney disease and neurologic problems, according to the FDA.

“If people develop bloody diarrhea or have a decline in urine output or are pale, they should seek medical attention,” says Shaw.

What experts need you to know: Consuming ground beef can potentially put you at a greater risk of E. coli exposure. “If you cook your steak, and you cook the outside, you’re usually safe from it,” says Parsonnet. “But if you make hamburgers, you’re taking the outside of the meat that’s been contaminated, and you're mixing it in the middle.” (The USDA recommends cooking ground beef to a safe minimum internal temperature of 160°F to destroy harmful bacteria.)

But it’s not just ground beef that’s linked to outbreaks. “A few years ago, there was an E. coli outbreak in apple juice because it was probably contaminated by feces,” says Parsonnet. Anything that’s contaminated with animal feces, such as produce grown in fields, has the potential to expose you to E. coli, she says.

Hepatitis A

What it is: A highly contagious liver infection caused by the hepatitis A virus. Exposure typically happens when people come into close contact with an infected person, as well as through eating or drinking food or water contaminated with the virus.

What the symptoms are: Lethargy, nausea, vomiting, loss of appetite, joint pain and dark-colored urine are all common symptoms. Clay- or gray-colored stool, as well as intense itching and jaundiced skin, are signs that can distinguish a hepatitis A infection from other foodborne illnesses.

What experts need you to know: Hepatitis A is rare in the U.S., thanks to vaccinations, notes Parsonnet. Adults who get hepatitis A typically recover within one to two weeks, but it’s possible for the disease to become chronic, which can lead to liver failure and death.

Shaw says that hepatitis A “is usually foodborne, either from contamination in the fields or with a food handler who is preparing food without sufficient precautions. Transmission can come from someone going to the bathroom and not washing their hands sufficiently and then preparing food.”

Recent hepatitis A outbreaks have been linked to strawberries, as well as raw scallops, frozen tuna and conventional blackberries.

Norovirus

What it is: A highly contagious virus that causes vomiting and diarrhea.

What the symptoms are: Norovirus causes nausea, vomiting, diarrhea and abdominal pain. “It usually resolves within two to three days,” says Shaw. These symptoms typically last one to three days, according to the Mayo Clinic.

What experts need you to know: Typically, people become infected after coming into contact with the virus by consuming food or drink contaminated by another person with the virus, or by coming into contact with a surface or object with the virus and then touching their mouth.

According to the CDC, norovirus is responsible for about 50% of all outbreaks of food-related illness, most of which happen in food-service settings such as restaurants.

“This is the virus that's associated with outbreaks on cruise ships,” Shaw points out. “It is highly contagious because the dose that you need to become infected is really low.”

Parsonnet agrees, adding: “If you have it, you can easily give it to your family and to other people in the household” through being in close contact, such as sharing food or eating utensils. Most people recover without treatment, but symptoms such as diarrhea and vomiting can cause severe dehydration.

How to recover from foodborne illnesses

The treatment for mild foodborne illness is typically rest and drinking plenty of fluids in order to avoid dehydration. In rare and severe cases, listeria and salmonella may be treated with antibiotics.

It’s also important to keep an eye on your symptoms, notes Parsonnet. A fever greater than 102°F, bloody diarrhea or diarrhea with mucus, bad abdominal cramps, weakness or confusion, and symptoms that don’t improve within 48 hours warrant reaching out to a health care provider.

This article was originally published on June 15, 2023, and has been updated.