Diners at Chipotle Mexican Grill locations on Saturday said freshness and convenience outweighed concerns about contamination following the news that food poisoning cases had erupted at the chain’s locations in six U.S. states. Shares of the fast-casual chain tumbled 12.3 percent to an 18-month low on Friday on word that the E. coli outbreak, originally limited to Chipotle locations in Washington state and Oregon, had spread to four additional states: California, Ohio, New York and Minnesota. At least 45 people have been infected with the E. coli O26 strain.