Health officials in New Hampshire are working to track down the source of an E. coli outbreak that has sickened at least 12 people.

Authorities said in a statement Friday that each case has been linked to ground beef, but the patients consumed the beef at several locations, CBS Boston reported.

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“The Division of Public Health Services is working with our federal partners to investigate the source of the ground beef that is causing people in New Hampshire to become ill,” Marcella Bobinsky, acting director of DPHS said in a statement, according to the report. “Ground beef is a known source of E. coli and it is important for people to avoid eating under-cooked ground beef whether at home or at a restaurant.”

E. coli can cause abdominal cramping, diarrhea, nausea, vomiting, fatigue and fever. Those who are elderly and young children are most at risk.