Because majority of the illnesses came from prepackaged vegetables that have been passed on from suppliers to distributors to processing facilities where they were chopped and bagged, finding out where they were grown is far more cumbersome.
“It's a labor-intensive task. It requires collecting and evaluating thousands of records; and trying to accurately reproduce how the contaminated lettuce moved through the food supply chain to grocery stores, restaurants and other locations where it was sold or served to the consumers who became ill,” Gottlieb and Ostroff said in their joint statement.
This is the worst outbreak since 2006, when 205 people became ill and five died from E. coli from baby spinach.
E. coli are a type of bacteria found in undercooked beef, raw milk, soft cheeses made from raw milk, raw fruits and vegetables, and contaminated water. Most E. coli bacteria are not harmful, but one type known as E. coli O157: H7 produces a toxin called Shiga, which destroys red blood cells, causes kidney failure and bloody diarrhea. Other kinds of E. coli cause urinary tract infections, respiratory illness and pneumonia.
Health officials said children under the age of 5, seniors older than 65 and those with weak immune systems are most vulnerable. So far, the outbreak has sickened people ages 12 to 84.