Salmonella infections linked to organic basil sold at Trader Joe's are under investigation. What to know about foodborne illnesses.

You might want to pick another week for homemade pesto. On April 17, grocery chain Trader Joe’s voluntarily removed all Infinite Herbs-brand organic basil, sold in clamshell packaging, from its stores amid an ongoing investigation by the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) into a salmonella outbreak. CDC data shows that 12 people across seven states have been infected; of those, at least seven people reported exposure to the fresh basil before becoming sick.

On April 18, Infinite Herbs voluntarily recalled 2.5-oz packages of its fresh organic basil sold between February 1 through April 6. On April 19, Infinite Herbs LLC expanded the recall to include Melissa’s-brand organic basil at Dierberg’s stores in Illinois and Missouri between Feb. 10 through Feb. 20.

Both brands of recalled basil are no longer available, and the basil should now be past its shelf life. However, the FDA warns that if you previously purchased this basil and then froze it, you should throw it away.

Foodborne illnesses are shockingly common. The CDC says that 48 million get sick from foodborne diseases every year in the U.S. Here's a guide to everything you need to know.

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 Dr. Julie Parsonnet, professor of infectious diseases at Stanford University School of Medicine. 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.

Dr. Albert Shaw, infectious diseases specialist and professor of medicine at Yale School of Medicine, 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.”

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 FDA.

What experts need you to know: “Listeria has the unfortunate property to grow under refrigeration temperatures, which is uncommon of foodborne illness,” Shaw tells Yahoo Life. “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, Parsonnet notes that the disease can be serious in certain individuals. “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.”

E. coli

What it is: Escherichia coli, or E. coli, is a bacteria that lives in the intestines of people and animals. 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 U.S. Department of Agriculture 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: Hepatitis A 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 fairly 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.