A multistate salmonella outbreak has been linked to ground beef, the U.S. Centers for Disease Control and Prevention warned Tuesday.

At least 16 illnesses have been reported, with six hospitalizations, the CDC said. Nine of the cases are in New Jersey, with five in New York and one each in Connecticut and Massachusetts. No deaths have been linked to eating the ground beef. 

“The true number of sick people in this outbreak is also likely much higher than the number reported,” the CDC said. “This is because many people recover without medical care and are not tested for salmonella.”

The first case was reported on April 27. Health officials have interviewed 14 of the patients about what they ate in the week before they got sick. Nine of them reported eating ground beef, according to the CDC. All nine of those patients purchased the beef from ShopRite locations in Connecticut, New Jersey and New York. Ground beef is the only common food the interviewed patients reported eating.

Seven of the nine people said they bought 80% lean ground beef. The two others who reported buying ground beef from ShopRite couldn’t remember the specific type. 

Investigators are still working to identify the source of the ground beef the sick people consumed.

Ground beef is a common source of salmonella; the germs live in the intestines of animals and can be spread through contaminated food, water, food preparation surfaces and unwashed hands, according to the CDC. Cooking ground beef to an internal temperature of 160 Fahrenheit kills salmonella germs. 

Reducing salmonella outbreaks from ground beef involves interventions at farms, slaughterhouses, processing facilities, restaurants and homes, according to the health agency. The CDC shared several safety tips, starting at the store while shopping. Keep raw ground beef separate from other food in your shopping cart and grocery bags. Once home, store it in a container or a sealed, leak-proof bag on the lowest shelf in the fridge or freezer. Wash any utensils and surfaces, including your hands, that come into contact with raw beef with soap and water.

Salmonella bacteria causes around 1.35 million infections, 26,500 hospitalizations and 420 deaths in the U.S. every year, according to the CDC. Symptoms can include diarrhea, fever and stomach cramps. Symptoms start six hours to six days after infection and last four to seven days.