CONCORD, N.H. (CBS) – New Hampshire public health officials are working to find the source of ground beef that has caused a dozen people to be infected with E. coli.

Authorities said in a statement Friday that since June, 12 people have come down with the same strain of E. coli after eating ground beef.

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Those people ate ground beef at several different places, and state and federal officials are working to identify the specific source.

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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,” said Marcella Bobinsky, Acting Director of DPHS, in a statement. “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 be life-threatening, especially in the elderly and very young.

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Health officials say New Hampshire residents are not at risk of contracting E. coli as long as they make sure their food is properly cooked.