Last week, federal officials announced recalls of ground beef and organic walnuts because they were potentially contaminated with E. coli bacteria that can make people sick.

The recalls involve more than 16,000 pounds of ground beef distributed by Cargill Meat Solutions and sold at Wal-Mart stores in 11 states, as well as organic shelled walnuts sold in bulk in natural food and co-op stores in 19 states. So far, the recalled walnuts have been associated with 12 illnesses, including seven hospitalizations, in Washington state and California.

No illnesses have been reported from the ground beef recall, although ground beef remains one of the most common sources of illnesses from these bacteria, which are responsible for an estimated 265,000 illnesses annually. Most of these, however, are not diagnosed or tracked by the Centers for Disease Control and Prevention because people often recover on their own without visiting a doctor, said Matthew Wise, chief of the CDC’s Outbreak Response and Prevention Branch.

Here’s what you need to know about E. coli to stay safe.

WHERE YOU’LL FIND THE BACTERIA

There are many different kinds of E. coli, and most of them are harmless to humans, said microbiologist Edward Dudley, director of the E. Coli Reference Center at Pennsylvania State University.

Some types do, however, make people sick, he said. Those that most commonly cause illness in humans, known as Shiga toxin-producing E. coli, primarily reside in cow intestines, which is why they often contaminate ground beef. The E. coli implicated in the ongoing walnut and ground beef recalls are a type of Shiga toxin-producing E. coli.

Because these bacteria eventually work their way out of animal intestines and into feces, they can also contaminate farm soil, which is why E. coli outbreaks are also often tied to produce, Dudley explained. They can also contaminate ponds, lakes and rivers.

Angelica Barrall, an Epidemic Intelligence Service officer with the CDC, said that the agency was still working to find out how the bacteria had managed to contaminate walnuts, which are grown on trees.

AN OUNCE OF PREVENTION

The best way to avoid getting sick from E. coli is to take precautions when preparing food, Wise said. Keep raw meat and poultry separate from other foods and wash your hands thoroughly after handling them. Cook meat and other proteins to the appropriate temperature to kill off bacteria that may be lurking inside, he said, and store leftovers in the refrigerator within two hours to slow bacterial growth.

Washing your hands often is a good idea whether or not you’re handling food, as E. coli can spread through contaminated surfaces or hands.

Since E. coli can sometimes contaminate raw foods — such as produce and nuts — it’s also important to keep an eye on food recalls and to throw away any recalled products, Wise said.

The CDC also recommends that people wash fruits and vegetables under running water, consume only pasteurized milk and fruit juices and avoid eating raw dough or batter. You should also avoid swallowing water while swimming in untreated water like lakes or rivers.

IF SOMEONE GETS SICK

People typically develop symptoms such as diarrhea, vomiting, a fever of less than 101 degrees and abdominal cramps within three to four days of consuming contaminated food.

These can be similar to the symptoms of other, more common foodborne illnesses, such as those caused by salmonella bacteria, which sickens an estimated 1.35 million people nationwide each year, or norovirus, which sickens an estimated 19 million to 21 million Americans annually. The bacteria Listeria monocytogenes, by comparison, causes only an estimated 1,600 illnesses.

One way to distinguish an E. coli infection from other issues is that people infected with E. coli often have blood in their diarrhea, said Dr. Robert Bonomo, a professor of medicine at the Case Western Reserve University School of Medicine.

Abdominal pain with E. coli is also usually worse than it is for other diarrheal illnesses, said Dr. William Miller, an infectious disease physician at Houston Methodist Hospital.

Wise suggested contacting a doctor if you or a family member have these symptoms or have had diarrhea for more than three days. Although most people recover in five to seven days without treatment, children younger than 5, adults older than 65 and people with compromised immune systems are at a higher risk for serious complications.

One potential complication is hemolytic uremic syndrome, or HUS, which can occur when red blood cell and platelet levels drop. This can sometimes lead to kidney failure, Miller said. HUS develops in 5% to 10% of those diagnosed with a Shiga toxin-producing E. coli infection, and among children, is most common in those younger than 5.

Doctors typically monitor patients for those complications and others, and try to keep patients hydrated until they recover. They typically do not treat infections with antibiotics or nonsteroidal anti-inflammatory drugs (such as ibuprofen), because these medications can increase the risk of HUS, Miller explained.

Anti-diarrheal drugs are a bad idea when you have E. coli, too. “You want your body flushing it out,” Dudley said.

This article originally appeared in The New York Times.

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